Moonshine

On the space colonization topic — I'm flogging the dead equine until the ivory shows — it occurs to me to note that currently, whenever someone asks "who's going to pay for it?" the answer is some variation on "the Lunar He 3 will make us rich!"

For those who were asleep when the Clue Fairy rang the doorbell, the narrative goes like this:

Helium-3 is a light isotope of Helium. It is of interest because, to crib from wikipedia:

Some fusion processes produce highly energetic neutrons which render reactor components radioactive with activation products through the continuous bombardment of the reactor's components with emitted neutrons. Because of this bombardment and irradiation, power generation must occur indirectly through thermal means, as in a fission reactor. However, the appeal of helium-3 fusion stems from the aneutronic nature of its reaction products. Helium-3 itself is non-radioactive. The lone high-energy by-product, the proton, can be contained using electric and magnetic fields. The momentum energy of this proton (created in the fusion process) will interact with the containing electromagnetic field, resulting in direct net electricity generation.

He 3 looks at first sight as if it could be the key to clean nuclear power — that is, to fusion reactors that live up to the original promise of not producing shedloads of high level waste. However, He 3 is vanishingly rare on Earth.

At this point, enter, stage left, a Space Cadet: He 3 is rare, therefore it's expensive. But there's He 3 in the lunar regolith, trapped there after being blasted out by the solar wind. We should go to the moon and mine He 3! It'll solve all our energy problems!

Unfortunately there are a couple of problems.

Firstly, nobody's built a commercially successful fusion reactor yet. ITER plan to build a working test-bed; it's logical successor would be a working prototype first generation power reactor. There are huge obstacles to overcome, not least in developing neutron capture techniques and breeding D/T fuel. These are engineering problems (sorry, annoying paywall) and theoretically amenable to solution — but at a price of billions of euros and decades of work, and even then, it may turn out to be too costly to be a viable competitor for well-understood fourth generation fission technology and a mature waste disposal/fuel recycling chain. And that's before we look to a speculative second generation reactor, running on a different type of fuel, that — because of the higher Coulomb barrier between He nuclei — requires a far higher temperature (on the order of 500M to 1Bn degrees celsius, rather than the relatively chilly 100M degrees C required for D/T fusion).

Given the average generation time for a new reactor technology of 20-30 years, and development costs on the order of $50Bn-100Bn per generation, we won't be even thinking about prototyping an He3 reactor until 2060 at the earliest.

Secondly, there's very little He 3 in the lunar regolith. The amount is non-zero, but we can also breed the stuff on Earth: Neutron bombardment of Lithium, Boron, or Nitrogen targets, or decay of Tritium are currently used. Breeding He 3 requires a high neutron flux, but unless the plan is to automagically shift us all over to a "clean" He 3 power cycle instantly, He 3 reactors will be coexisting with "dirty" high-flux fission or fusion reactors for many decades.

Is it really going to be cheaper to send monster trucks to the moon, than to build a couple of special-purpose high neutron flux reactors optimized for mass production of Tritium (and thereby for production of He3 as a decay product)?

The whole Lunar He 3 mining proposition is a boondoggle, based on wishful thinking: that (a) we can make a working commercial fusion reactor (not yet proven, and will cost some tens of billions of dollars to get to that point), (b) if we run a more advanced — and much hotter — reactor on He 3 it produces somewhat fewer secondary neutrons, (c) He 3 is vanishingly rare on Earth but there is a tiny amount of He 3 in the Lunar regolith, so (d) MOON!!!11!!ELEVENTY!! WITH MONSTER TRUCKS AND BULLDOZERS!!!

He 3 is not magic high-energy pixie dust. And in the context of the space colonization debate it should be seen for what it is — a placeholder for the alchemist's stone that will turn the money-hole of a lunar colony into a profit centre: an extractable natural resource that can't be found on earth and is valuable enough to mine elsewhere. Unfortunately, the harder you look at the value proposition, the more it comes to resemble a pig in a poke.

Unfortunately for us 99.999 recurring a lot percent of the universe that might or might not have something we can exploit is 100% out of our reach. Forever.

Reachable space is our own back-yard, the moon, Mars (with a lot of effort) and just conceivably the asteroids and the Jovian system (with autonomous machines) and the cost-benefit ratios dive to near zero by the time you get out there.

I'm about as big a spaceflight junkie as you're likely to meet, but in all honestly, going out there because, financially, it's worth it... Nah!

It would be nice if one of your links had been to a Space Cadet saying "the Lunar He 3 will make us rich!" so that this series didn't look quite as much as though you were trolling straw libertarians.

Also, saying that "currently" the above is the answer is strange, given that my second search result after Wikipedia for lunar He3 is a page seemingly from 1999, which also has a few more calculations than you do: http://www.asi.org/adb/02/09/he3-intro.html

Serious question. As an ICBM platform the lunar nearside sucks -- anyone can see you coming as soon as you launch, days in advance. Farside is more practical, but is vulnerable to pop-up first strikes coming over a horizon that is much closer than it is on earth, hence there's less warning time. And as for an observation platform, the moon is a whole lot further away than a spysat in polar LEO.

About all that's left is prestige -- and why squander it on a display of militarism when even a civilian presence says "look what I could do, if I felt like it"?

As I said above: you could theoretically drop rocks. Big rocks. The problem is that I don't think that you could make dropping rocks cheaper than launching ICBMs from Earth.

The moral of the story is that space is not built on human scales or in a fashion that lends itself to human exploration. My solution to this problem is to radically alter what we mean by "human". People don't seem to like that response, though. And it does nothing to address the ridiculous energy costs of going into space.

The problem is that I don't think that you could make dropping rocks cheaper than launching ICBMs from Earth.

If cost alone were the object, it could still happen -- various militaries have been known to do very expensive things when a cheaper solution would suffice. Real problem is that dropping very big rocks from the Moon requires building a very big structure on the moon, which is VERY conspicuous[1] and by its very nature quite vulnerable -- you only need to damage it a little to render it inoperable. If China (space cadets' favorite boogaboo) were silly enough to build such structure, US would spend a fraction of its cost on small robotic missiles hidden either on the Moon or in Lagrange points, ready to wreck that structure.

what use is a military moon base?

I asked this question on Bad Astronomy board. The responder actually understood the futility of putting offensive weapons in the Moon; his answer was "command and control base, far enough from the main hostilities to survive a nuclear first strike". But above objection stands -- such manned base would take a decade or more to build, which gives more than enough tme to develop unmanned countermeasures.

[1] Keeping the location of Second Catapult (basically a humongous electromagnet) secret was the single biggest error in "The Moon is a Harsh Mistress". Heinlein could be excused for not knowing just how hard true AI is; he should have known that firing that catapult would be like lighting up a neon sign to some very basic magnetic sensors.

He-3 mining on the moon is something of a chicken and egg problem. Mining it would be cheap if we had clean fusion rockets and reactors to get us there. Which would be affordable if we had cheap He-3.....

Still, I suppose if we could come up with a nuclear fusion rocket then reaching space would be easier and cheaper. And we'd have a reason to go there.

Of course, that means we just need to perfect a yet-to-be-invented technology. With chemical rockets it doesn't make much economic sense though.

That's sort of the problem with all space colonization plans -- they assume some unknown economic benefit such as microgravity manufacturing or lune He-3. But if you look at colonial history on Earth, the original explorers and colonists already knew what the economic benefit was. Columbus was looking for trade with India and had to do some fast-talking when that wasn't forthcoming. Fortunately a lot of gold was discovered making further investment worthwhile. The original English colonies in North America were private ventures looking to make money off of things like fur. The company backing the Plymouth colony expected them to return a certain number of furs each year. The *colonists* had their own reasons for going but the people paying for it expected a return.

Allen Steele's "Tranquility Alternative" had a military moonbase built during the Cold War by the US. The idea was that it was a second-strike capability. No one could launch a preemptive strike against it because the missiles would be seen coming. And it couldn't launch a preemptive strike either. But in the event of a nuclear war it could get some sort of revenge on whoever attacked the US.

Of course, the book also featured it being sold off to a private company in the 1990s since it was a big waste of money mothballed years earlier. :)

It would probably be cheaper and more practical to build a military base at the L4 and L5 points rather than the moon's surface. Same distance and no gravity well to worry about. Fill them up with missiles and a C&C base. Maybe even some manned satellite-killers.

Allen Steele's "Tranquility Alternative" was a beautifully depicted what-if based on Wernher Von Braun and Willy Ley's 1950's Time-Life book "From the Earth to the Moon". Alterate history based on the idea that that particular version of the first Lunar expedition gained traction in 1957, rather than Apollo.

Also, and this is was explained to me by an acquaintance who studied space engineering, mining anything on/from the moon comes with yet another subset of problems related to its mass. If you start to bring back mass to Earth, you'll (apparently)soon run into the issue of the moon's orbit changing, which would cause tsunamis (good for extreme surfers) and other unpleasant weather effects...

PS. on a different topic which may be of interest: According to OMX (the Scandinavian stock exchange, 30% of trading is today done by algorithmic software and not people. It's constantly growing. It's also smarter and much much faster than people.

Other than the general "It's a cool thing to do", I can't think of any profitable reasons to go to the moon. On the other hand, it would seem that there are potential benefits from micro-gravity environments (space stations) that will probably be realized. For the most part, these benefits will also be amenable to production through robotic means.

He-3 actually has practical application in exotic cryocoolers, and as a result one can buy the stuff. The last time I checked, it was US$250/liter. Show me a way to way to extract the stuff from regolith (and I'm not convinced that there's enough there, either) for less than that and I might be willing to have a discussion on the topic. But given that it's still US$10000/lb to LEO....listen, if you can reduce launch costs by two orders of magnitude, you don't need fusion power.

As well as the physical analysis, we need an economic one:
"He 3 is rare, therefore it's expensive."

Well, let's presume we can mine it off the Moon and make use of it on Earth. What happens to the price when it is no longer so rare? Quite possibly, it plummets, wrecking the economic return from any proposed lunar (or Neptunian ) mining.

Well, the Earth's gravity well is deeper, so it will always be more expensive to get, say, a nuke from the Earth to the moon. But you can still, pretty easily, get the nuke there. And on the Earth, you have a massive industrial base, which is lacking on the moon. And anything you want to bring to your base to harden it has to originate on Earth to begin with. Since you can't really "live off the land", that means you're going to have a 363,000km supply line, governed less by geography and more by orbital mechanics.

So, really, if anyone wants to take out your moon base, all they need to do is engage in enough attrition to make your supply line too expensive to maintain. Or, they could slip a nuke in with your regular traffic.

At the moment, no. But in real life, should China (or anyone else) start building something on the Moon, or even seem like it might build something on the Moon, US would produce something alone the above lines very quickly, and at a tiny fraction of a cost of manned base.

And in TMIAHM, given the amount of space traffic, it would be trivial to monitor Moon for magnetic activity.

Atually i had a similar experience during a university seminar. the seminar was entitled "science in society" and the class was mainly filled with human hating eco-warriors. At one point a discussion was started over the threat of moon mining (IIRC for both he3 and easily available nitrates) to the environment. Indeed the professor kept suggesting it was a pressing issue that should have some sort of ban put in place before we change the moons orbit and damage the earth through disasters such as flooding and tsumamis. when i suggested that a kilotones of matter being removed from the moon wont matter at all i was shouted down by classmates for not caring enough about the environment and told i wasn't thinking long term enough by my prof!

What about the asteroids? (My own idea: use something like a really big mass spectrometer to do unattended atomic sorting of asteroid plasma into buckets of pure elements that can be pushed onto the interplanetary transport network and drift their way slowly but cheaply back to earth.)

Seems to me the question is whether you could build the base so that making the counter-measures was equally expensive. Then you've got the potential for it to come about as part of an arms race.

Let's see. An ultra-expensive, never-before-done engineering project in an extremely hostile environment, completely cut off from physical contact with its engineering base and labor pool except for extremely expensive and massively latent refreshes. Now harden it.

The history of warfare, along one dimension, is the history of static defenses being overcome by directed force. So far, static defenses always lose. I don't see how this changes when you put them on the moon.

In fact, it seems like the perfect sort of thing to encourage your enemy to get up to. In effect, they invest heavily on playing on a chessboard you don't care about, while you get to watch. If you ever do start to care, they've already worked out at least some of the hard parts.

I'm running on three hours' sleep, so I'm going to skip all the comments, and just ask for the t-shirt. Can I please get "MOON!!!11!!ELEVENTY!! WITH MONSTER TRUCKS AND BULLDOZERS!!!" in an adult medium? Anybody? I promise to wear it at cons.

I still can't see how you'd get a realistic ROI on any naturally occurring raw materials I can think of... (with our current or likely near future level of tech). How much stuff are you going to need to cart out there? How many $BILLIONS will it cost?

If there were something super exotic and rarer than unicorn horn here on Earth, that suddenly became essential, then maybe, but I can't see what that might be.

History is already chock full of money sinks. The US government (given it's past and current spending habits) is a prime example of how to waste money. But little of this matters, because in my humble opinion, we've entered what I like to think of as the technological dark ages (a lot of fields have been advanced about as far as they are going to be). Or the art deco phase of technology if you prefer (i.e. Apple).

My current favorite example of technological stagnation:
The intel commercial "generations" where the closing line is "it's boosting performance automatically..." which loosely translates into we are powering on the floating point unit at this time, because if we clocked these circuits continuously, your electric bill would double, although there is the advantage of your home computer doubling as a space heater in the winter.

Pinch me, I must be dreaming, such an earth-shattering technological advancement in computing coming out of Intel.

If I have to dream, let it be of another generation that will at least try to get off this rock, perhaps merely because they've become fed up with the stupidity of the way things are.

And in the context of the space colonization debate it should be seen for what it is — a placeholder for the alchemist's stone that will turn the money-hole of a lunar colony into a profit centre: an extractable natural resource that can't be found on earth and is valuable enough to mine elsewhere.

It has basically the same problem that all the plans for commercial space ventures beyond LEO have: exorbitant capital expenses with little to no guaranteed commercial payoff for the people back on Earth.*

You tend to run into the same type of stuff with asteroid mining. Sure, you could probably land on one, but you still have to get enough material down from the asteroid to Earth to make it worth your time, without dumping so much of that material that it collapses the price and destroys your market.

* Of course, asteroid and moon mining would be very good . . . for supply already existing off-world colonies.

The history of warfare, along one dimension, is the history of static defenses being overcome by directed force. So far, static defenses always lose. I don't see how this changes when you put them on the moon.

Keep in mind that interception technology (in the form of anti-missile technology in particular) has gotten much better as well. Factoring the distance, it probably wouldn't be much more expensive to put a geosynchronously linked satellite with anti-missile capabilities in orbit directly over your Moon Base.

Of course, there's stuff that won't help with (like if your opponent is potentially aiming huge solid-state lasers at your moon base from LEO), but it's something.

Military use of the moon? Carpet areas with solar-powered lasers, of course. Spread the damn things like weeds.

Why?

If you armor the power storage and laser units (especially if they're away from the conspicuous solar arrays), they'll be a pain to destroy, because you'll have to generate enough debris to kill the entire field of solar arrays, and play find the laser before it finds you.

It's akin to the old, musket-based army strategy: laser broadsides from huge massed forces that are difficult to entirely destroy. And you don't see the flash coming, either.

You could, of course, tune the lasers to transmit power to the Earth, but people might get whiny about that. You could also use the lasers to power Earth-Luna space traffic (lightcraft, natch), but who needs nice, peaceful uses when we can kill people? (/Sarcasm)

Have space elevators been utterly debunked as a potential method of getting the hell out of the Earth gravity well?

No, but they suffer from two problems: (a) the unobtanium requirement (and other trifling engineering obstacles like, er, how to power a climber thousands of kilometres overhead economically and efficiently enough to make GTO in something less than months; how to survive transiting the Van Allen belts slowly: how to deal with rogue satellites and other debris: and so on) and (b) the fact that almost all the launcher development money is currently going into approaches that are known to work, i.e. disintegrating totem poles.

I have a soft spot for space elevators and they should, in theory, solve a lot of our problems with access to near space -- but I've got a bad feeling they'll cost as much and take as long to develop as commercial fusion power.

On the other hand, the biggest obstacle -- materials with a high enough tensile strength to support an elevator -- are theoretically possible if we develop fullerene materials further, and at every step of the way the intermediate materials will find a market. Fusion power has a huge multi-billion dollar gap to span before we go from lab experiments to an actual revenue-positive power station. Whereas incredibly strong cables suitable for use as bridge stays are instantly useful, even if they're only iteration 3 out of 15 needed before we get to a space elevator-grade fibre.

Colonizing space is easy. It simply requires a paradigm shift akin to the change from throwing spears to using smart missiles. In other words, we'll have easy access to space only after we develop cheap antigravity, or something similar. If you're a space cadet, don't bother with "economic analyses of helium 3" or any such bullshit. Get with the paradigm shifting. (Personally, I'd suggest checking into current advances in semi-conducting and materials science, but there might be other neat stuff out there that could be massaged into a major paradigm shift in less than a hundred years...)

Meanwhile, Charlie, for purposes of writing science fiction, authors are traditionally allowed a handwave or two, plus reasonable extrapolation of current technical trends. The important thing in any book is the characters and how they react to their situation - for example, computational demonology is clearly bullshit in the real world, but the fact is we like Bob Howard, and he was caught up in a cascade of horrible failures, then had a really bad experience which left him with life-altering PTSD... We can all relate to that and sympathize with the character.

The accuracy of science-fictional fantasizing in your books is completely irrelevant to why we like reading them. As long as the "science" (and I use the term loosely) is self-consistent, and you don't tech the tech with still more tech, we'll be happy to read your stuff. Or to put it more bluntly, we like the Eschaton stuff just as much as we liked Halting State, and for the same reasons - you built characters we could like/relate to and had them face difficult challenges. The scientific accuracy of the worlds they live in... who cares?

The only viable short-term answer to "who pays for Lunar settlement" is "space tourists." Right now we have people willing to pay $20 million and give up a couple of years of their life to go to orbit. If and when launch costs fall to the point that going to the Moon is in that (inflation-adjusted) ballpark you'll see some small private colonies.

Longer term, Not In My Backyard (NIMBY) is a powerful force. Mines and refineries are dirty and dangerous. Moving them off-world will start to make sense, if launch costs go down significantly.

This is where the Space Cadets put the cart before the horse. At current launch costs, space travel of any kind is horribly expensive. But there doesn't appear to be any engineering reason that launch costs have to be high.

We have evolved on a planet with a gravity well that is annoyingly difficult to climb out of.

On the other hand, the depth of the gravity well is precisely why we were able to evolve in the first place -- it prevents solar UV splitting of water vapour into hydroxyl radicals and hydrogen from rapidly desiccating the biosphere.

And some of the problems are of our own making. For example, I'm pretty sure we could build reusable SSTO spacecraft right now -- if it was politically acceptable to use NERVA with liquid nitrogen as reaction mass. (LN2 is a damn sight easier to handle than LOX or LH2 -- higher boiling point, for one thing: not explosive or an oxidizing agent, for another -- and you ought to be able to get a somewhat higher specific impulse by feeding it through a nuclear reactor than you can get from LOX/LH2 cryogens.)

Aside from what Ilya noted re: orbital dynamics, my point about static defenses always losing is really a note about economics. What is working against you there is the inherent nature of the game: protecting something of value in a known location against all out attack is extremely difficult: the defender has to always win, whereas the attacker only has to win once. Add in that you have to worry about maintaining a closed biosphere (unless I missed a post about the evil robot army), and that sitting on the moon rather limits one's supply lines, and you have a pretty big problem, no matter how nifty your Star Wars program is.

Of course this is all a bit silly; absent an economic reason to armor up on the moon in the first place, there's no military reason to stick a really, really expensive chess piece over a light second away.

extractable natural resource that can't be found on earth and is valuable enough to mine elsewhere. Unfortunately, the harder you look at the value proposition, the more it comes to resemble a pig in a poke.

At $38000/lb, rhodium seems to have some decent margin for profitable lunar mining even with current launch costs and no cross subsidies. Platinum too.
Lunar mining would be for asteroid impactors with high concentrations of these metals. Viability will depend on mining and extraction techniques and costs.

More importantly, reduction in price/increase in quantities could open up new industries, e.g. platinum based fuel cells.

The biggest issue is upfront capital costs, so I don't expect this to happen until we know how to get to the moon efficiently without national space agencies. In practice I suspect that asteroid mining might be easier, but there is an advantage to having teleoperated mining and refining equipment that can be run from earth or, worst case for delicate operations, lunar orbit.

There have been other - and purely science-fictional - resources that would be economically worthwhile going after. Sheffield and Varley both had black holes prefiguring as energy sources and there were hole industries based upon finding these wee beasties and bringing them back home. There are also monopoles, which have some pretty exotic properties and which seem very, very valuable, also found only in space and usually in the interiors of asteroids. And if you go very, very far back, you'll find stories about large chunks of antimatter (they called it seetee back then) scattered here and there in the solar system.

All of these seem to be plausible candidates for massively gearing up a presence in space and grabbing the loot. All them are also of course, purely sf at this point.

I have a soft spot for space elevators and they should, in theory, solve a lot of our problems with access to near space -- but I've got a bad feeling they'll cost as much and take as long to develop as commercial fusion power.

It seems there's a whole bunch of these mega-scale projects that tweak space fans in a very idiosyncratic way. Me, I'm indifferent to the elevator, but I love those space fountains - essentially, shooting canon balls up into space and magnetically coupling a support structure to them. They don't require exotic materials in bulk quantity (where's my arenak-armored flying car?), and they pose some interesting problems in getting started that aren't known to be insurmountable.

At $38000/lb, rhodium seems to have some decent margin for profitable lunar mining even with current launch costs and no cross subsidies.

Can't say I see it. Being a modern expert in all things, I googled around for five minutes to see what the refining method for rhodium is. Without even looking at the difficulties of mining on the moon, and assuming you're also recovering the platinum it normally occur with, simply refining enough rhodium of both to pay to boost a refinery plant to the moon would easily tank your $8.8B global market. For reference, the lowest estimates I've seen for the cost of the ISS are $35B.

True, having a catalytic converter for my cigarettes would be nifty, but that's an externality. I don't see how you finance and insure the exploitation of a self-destroying market like that.

Separation of platinum group metals is done by pulverizing rocks and solvent extraction. This is not that complex, especially as the metals only need to be refined on earth from the extract, not on the moon. Acid extraction on the moon sounds a lot more environmentally friendly than on earth too.

What the cost of the ISS has to do with anything is beyond me, I assume this was thrown in as a red herring.

I don't think you've addressed the most limiting part of space exploration. That being the meaty bags of water we're so determined to stick on the red planet. That is, the human problem.

Firstly, spending much time away from earth's orbit is fatal. Even if you don't die you'll wish you had by the time you reach Mars. Detached retinas and a guarantee of fatal cancers within ten years by the time you got to Mars. Unlike the Earth Mars doesn't have that molten core of metal that protects us all from the sun's radiation.

Shielding a ship properly is impossible with current technology. Get back to me when you have a space elevator. We're talking about a dozen international space stations in lead, and then the fuel and rockets needed to get that much mass moving.

Secondly, no one has ever succeeded in making a sealed biosphere work. I think it's puzzling that people want to go explore other planets when we haven't even got this one properly figured out.

Finally, and most compellingly, those biosphere experiments have all proved that if you lock a small group of humans up in a small space they all go bugfuck insane. They did get some interesting data on human nutrition out of it though, so not a total loss.

@53:
Mining Platinum or Rhodium on the moon has the exact same problem as on Earth: this stuff is rare! Even worse, while Earth was subject to large scale entropy reducing processes (known as tectonics, weather and LIFE) there was little of that on the moon.

Except for meteor impacts and ancient volcanism I don't see a lot of potential for ore-formation of anything on the moon, so your Platinum is likely to be stochastically distributed and even harder to find and mine than on Earth.

@50:
Erm no. Nerva with nitrogen doesn't make sense (unless you're trying to build a nuclear air-breathing ramjet). Why? The way it works is by heating gas. The temperature is constrained by the reactor itself, so you'll get the same temperature regardless of the gas you use. Now, Physics tells us about the energy of a gas: E =p*V= n*k*T

n is the number of molecules in the gas, p*V represents the energy you could gain theoretically, by expanding the gas to a pressure of zero. The higher the temperature, the more energy you have. But temperature is a given, so is the Boltzman-constant k. In order to maximize energy per mass, you have to increase n. The only way to do that is to use as light a gas as possible. N2 is 14 times as heavy as H2 and since exhaust speed is proportional to the square root of energy, you'd reduce specific impulse by a factor of 3.75 to something that couldn't quite compete with the Space Shuttle solid rocket boosters.

Even H2O, which is significantly lighter than N2, would result in a worse specific impulse than the Space Shuttle Main Engines, which burn at higher temperatures than Nerva can reach and use excessive amounts of H2 that is only heated up without being burned (for lack of oxygen).

By using hydrogen instead of water, specific impulse immediately goes up by a factor of 3, because it is 9 times lighter.

Oh and btw, I have a soft spot for maglevs in long vacuum tubes. You could accelerate a rocket in one of those to 2-4 km/s and send them up on the side of a mountain. The top end would be sealed by a rubber membrane to keep the vacuum inside the tube, but allow the rocket to crash through it without being damaged. The extra speed should be enough for SSTO. The cost of electricity needed to accelerate the train to this speed is marginal.

The rest would be an exercise in building a cheap disposable maglev or building the maglev rugged enough that it can withstand the g-forces of going over the mountain ...

Enter computing with superconducting chips (e.g. Josephson junctions). Use the extreme cold traps at the lunar poles to site huge server farms drawing relatively little energy to process the ever expanding data generated on earth. Transmit the results back to earth for the earth based server farms for low latency information access.

Large high energy physics facilities requiring superconducting magnets and vacuum would be more scalable on the moon. Likewise, fusion reactors could be built there for the same reason, although the energy produced may never be competitive with earth's own sources, but more useful to space infrastructure where energy is expensive.

That doesn't work either. Because stuff is only cold if you can keep it cold. The only way in which you can keep something cold in space, is through radiative cooling - which is a rather slow and inefficient process. Not even enough to keep an IR detector chilled - not to mention a computer that is actually doing stuff.

The other way is by dumping heat into something big and cold. But show me a cold asteroid and I show you the decaying Uranium and Thorium heating it up above 5K.

Mining Platinum or Rhodium on the moon has the exact same problem as on Earth: this stuff is rare! Even worse, while Earth was subject to large scale entropy reducing processes (known as tectonics, weather and LIFE) there was little of that on the moon.

Platinum group metals are not formed by terrestrial ore forming processes, but are associated with impact sites, e.g. the Sudbury mine.

On the moon you would locate the impact site of metal asteroids and look for platinum rich ejecta. Thus the moon is as reasonable a site as earth for platinum group metals.

The issues are not rarity, but the cost of extraction of concentrates of these rare metals. There is also the issue of demand, with very finite limits of production on earth.

But the energy required to keep a superconducting chip running is much lower than silicon transistors. Of course you have to cool the waste heat radiatively - but fortunately the universe is a rather large, 3.8K, heat sink! (There is also a lot of metal on the moon to make those radiators. Perhaps they could even use platinum ones, if Terra isn't buying that month).

I was working as a student programmer at the US Department of Energy's Argonne Labs around '76. At the time, all the nuclear engineers were pretty confident that reliable and commercializable fusion power was only 20 or 30 years away.

It's now 34 years later. We still haven't managed a single net-energy-positive fusion reaction in the lab AFAIK. But commercial fusion power is still only 30 years away!

That's not as bad as AI, which has been "only 20 years away" for 60 years now, but it's bad enough to make me highly skeptical about the profitability of lunar mining He3 before we actually need the stuff in vast quantities. This would be, as Charlie pointed out in the first place, two generations of major technology away. Charitably assuming that the 30 years for commercial fusion power is actually right, this time, and that advancing to the next generation would take a similar time, I say that would make our timeline for possibly needing He3 in volume more like 2105: 30 (more) + 65. This is not what I would view as a priority.

I think there is some magic power about the timespan of "20 or 30 years" which makes even hardened scientists assume that all known problems with a technology will surely be tractable in that time. Of course what they don't know is all the intractable or merely difficult problems that are sure to come up while trying to actually solve the problems they currently know about. While 30 years can be a long time in science, if we optimistically assume Ph.D. theses take about 5-7 years, that's only 3-6 generations of research to build on each other, so it's not as long as it seems like.

Of course I do. What I'm questioning is why you think moon-metal is economicly for making them.

Separation of platinum group metals is done by pulverizing rocks and solvent extraction. This is not that complex, especially as the metals only need to be refined on earth from the extract, not on the moon. Acid extraction on the moon sounds a lot more environmentally friendly than on earth too.

What the cost of the ISS has to do with anything is beyond me, I assume this was thrown in as a red herring.

I'm not questioning complexity. We're pretty good at putting complex things in space.

I'm questioning the economics, and that's where the ISS comparison comes in. It is all about the throw weight to get a refinery online, on the moon.

Not being a refinery general contractor, I couldn't tell you what the smallest sensible extraction facility looks like, or more importantly, what it weighs. But I suspect a closed-loop facility for smashing rocks, bathing them in solvent, bottling the resulting slurry and packaging it for "repatriation" weighs a goodly fraction of the ISS. Then, factor in the mass of the solvents, or a factory to make them, if that is possible, on the moon, the trucks to move the ore, support infrastructure for people to find the ore, the diggers to get to the ore, spare parts for all of the above...

So you have a baseline cost for extracting your goodies. it sits on yield curve. If the earthbound price falls below the minimax of that curve, you're losing money. There's the limit on your cost recovery, measured in lb/time.

If you plot that, I strongly suspect the break-even is quite a bit further out than the time horizon of just about anyone who isn't immortal. And to even finance it, you need to insure it, and as the break-even moves outwards in time, your insurance costs go up.

I, too, have a soft spot for Space Elevators. However, I was discussing this topic with Jordan Kare last weekend and he dropped another couple of gotcha's on me that I hadn't thought of .

The Unobtanium not only has to deal with the huge loads, but also non-trivial twisting moments in the cable AND extraordinary thermal differentials between the side in the sun and in shadow.

He said they'd done some BOE calcs to show that the cable would be oscillating between 20K(ish) to 500K(ish) pretty much instantly as the cable twisted. He suspected that that would be bad for any conceivable form of Unobtainium that we're working on :(

Not being a refinery general contractor, I couldn't tell you what the smallest sensible extraction facility looks like, or more importantly, what it weighs. But I suspect a closed-loop facility for smashing rocks, bathing them in solvent, bottling the resulting slurry and packaging it for "repatriation" weighs a goodly fraction of the ISS. Then, factor in the mass of the solvents, or a factory to make them, if that is possible, on the moon, the trucks to move the ore, support infrastructure for people to find the ore, the diggers to get to the ore, spare parts for all of the above...

But does it really?

How is ore leaching done on earth? You pile up your crushed rock into a pile, pour acid over it and allow to percolate, then tap of the metal "concentrate" from the collecting ponds.

What about the moon? Firstly no need to expend machinery crushing rock, because several billion years of impacts have done that for you. Hence those lovely moon buggies throwing up dust plumes mining He3 in "Moon".
So now maybe all you need is a rover, scooping up regolith and filtering off the large rocks leaving the fines. Here the gravity helps to make high, steep piles.
Put the fines in a large, but lightweight container that can be sealed to keep some air pressure. Add the acid and tap of the slurry.
Vacuum distill the slurry (free vacuum and sunlight) to recover the solvent leaving metal salts that you want.
process further if economic and ship back to earth.

Now I don't see massive rock crushers or movers being needed. Nor a huge processing plant. No EPA worrying about ground water pollution. Nor is there any need to be very efficient, just extract what you can and forget about the rest.
No people living on the moon, everything done robotically or telechirically. This is mining simply, with minimal resources. It isn't efficient or "neat", but that isn't a requirement.

In time some of the simple equipment could be made on the moon: filters (metal wire grids), vacuum distillers (glass & metal tubes).

My guess is making the acids locally will be the hard part, not the metal extraction.

Now what about demand?

Suppose I asked the market for 100 tonnes of platinum a year, for 20 years starting in a decade. Could the market do it? Probably not, because there isn't the resources available on earth, no matter what the price.

Should such a demand emerge, or supply emerged to fuel that demand, extraterrestrial resources would be needed.
There could be no undercutting of price by low cost producers, as they do not have the supply, so terrestrial producers would be price takers, not makers.

Hurrumph... still think entirely possible that the benefits of mining in space will never justify the cost.

Why? Well it neatly answers Fermi Paradox because if cost exceeds benefit (and money just a proxy for the effort:reward ratio) then space travel isn't self-sustaining, which explains why universe isn't full of intelligent life just bumming around the stars.

If effort of going into space could be made to work and generate a return greater than effort then you'd just need one civ to do both that and get to neighbouring stars and they'd fill the galaxy - given that this hasn't happened even with all the stars in the galaxy this suggests some fundamental physical property means it just don't work.

And it's probably that the sheer effort of maintaining civilisation outside of a convenient self-sustaining biosphere you've evolved into is just so great that no return you get is worth the effort.

So Fermi shows that there is no point going into space.

Solved it for you.

(I rambled along similar lines on another thread on this site last week, promise to stop banging the drum on this one after this post)

It seems there's a whole bunch of these mega-scale projects that tweak space fans in a very idiosyncratic way. Me, I'm indifferent to the elevator, but I love those space fountains - essentially, shooting canon balls up into space and magnetically coupling a support structure to them.

Heh. Here is my favorite:

In "Camelot 30K" Robert Forward describes a very ingenious propulsion system, which can send people to Outer Solar System and theoretically can be built with today's technology, but certain "technical problems" must be addressed first :)

An enormous electromagnetic rail gun in Earth orbit, powered by a fission reactor. By "enormous" I mean the rail is 4000 km long, and IIRC is smelted from an iron asteroid. It could be much shorter for unmanned payloads, but is that long to limit acceleration to 10g for human passengers. A simple calculation shows that accelerating a payload at 10 gravities for 4,000 km will throw it at 28.3 km/sec. Question is, how do you stop?

This is the ingenious part. Long before human spacecraft is built, a second, somewhat smaller catapult is made, and is placed into a higher, elliptical orbit. A supply of iron slugs is delivered to (made at?) Catapult A. Catapult A launches a slug directly at Catapult B. Catapult B catches it in its railgun, thus transferring momentum. Catapult A keeps firing slugs at such points in its orbit so that reaction vectors mostly cancel out, and Catapult A's orbit does not change much. OTOH, Catapult B keeps getting hit near apogee, so it keeps receding. Eventually Catapult B reaches escape velocity. As it moves away from Earth, it keeps catching slugs, for years if necessary. Some ten years later it reaches it destination (in "Camelot 30K" a hypothetical KBO, but it could be an accurate description of Eris). When it gets there, Catapult B fires off its entire load of slugs to decelerate and enter orbit. When manned capsule arrives, Catapult B catches it. It can be smaller than Catapult A because the capsule moves somewhat slower than 28.3 km/sec by the time it is in Kuiper Belt.

So you go from "won't work" to "well it's cheaper to do it on earth, so why bother".
You wanted to shoot down the idea by making a numerical computation to debunk it. That was invalidated by not thinking through how it might be constructed. Resorting to an economic argument is silly, since I never claimed it would be economic.

Or, then, there's Cavorite .. Never neglect Cavorite, which has been around for ever such a long time ...

" The society and persons in the story may be ordinary, but faced with bizarre circumstances such as the invention of teleportation, or the discovery of a new chemical element with unusual properties (such as Cavorite in The First Men In The Moon). "

This after a swift Google and the memory of having watched ' Things To Come ' in DVD the other evening ... BIG shoulder Pads ..POWER DRESSING !!!! How did they anticipate the 1980s way back then ? ....... " TO THE GUN !!!! "

It is My own thought that the 'Clue Fairy ' has far too narrow a Career Path and that He, She or It Should be Delivering Fully Formed Cold Fusion Reactors to those of us who truly deserve them and have been GOOD Boys and Girls all year.

Phooey to all this HARD Science Stuff ..I think back upon the Delights of Cold Fusion every time I receive my bill for Electricity.

Without Cavorite type Magic we will need to make the First Step in Technology before all the others and so What will we need to do to produce the materials that will make the first Magic Mushroom Step possible and how long is it likely to take us before we achieve that first step?

As a Spur to First Step and beyond the only thing that I can think of is a Sure and Certain way that an orbital, and beyond, platform in the High Frontier will be driven a furious speed is a Discovery of a Space Born Technology that will extend the personal life spans of the Extremely Rich.

Forget about rare metallic STUFF .. what is more valuable than Life itself?

There you go, dragging Carnot efficiency and the Stefan-Boltzman Law into the mix...working in a research reactor gives you access to all sorts of ancient documentation, including the one I'm reviewing currently. "This booklet is one of the "Understanding the Atom" Series"

The predictions made in this one were as follows applying mainly to the use of nuclear reactors in space):

1) Large orbiting space laboratories - launchings could begin about 1972.
2) Lunar exploration following the Project Apollo lunar landing...the establishment of a permanent base on the moon in the late 1970's.
3) Scientific recon of the nearer planets (especially Mars) with large unmanned landers, followed by manned landings, possibly in the 1980's.
4) Large unmanned earth satellites for a variety of purposes...(solar cells may compete here)

How is ore leaching done on earth? You pile up your crushed rock into a pile, pour acid over it and allow to percolate, then tap of the metal "concentrate" from the collecting ponds.

What about the moon? Firstly no need to expend machinery crushing rock, because several billion years of impacts have done that for you. Hence those lovely moon buggies throwing up dust plumes mining He3 in "Moon".

So now maybe all you need is a rover, scooping up regolith and filtering off the large rocks leaving the fines. Here the gravity helps to make high, steep piles. Put the fines in a large, but lightweight container that can be sealed to keep some air pressure. Add the acid and tap of the slurry.
Vacuum distill the slurry (free vacuum and sunlight) to recover the solvent leaving metal salts that you want.
process further if economic and ship back to earth.

Now I don't see massive rock crushers or movers being needed. Nor a huge processing plant. No EPA worrying about ground water pollution. Nor is there any need to be very efficient, just extract what you can and forget about the rest.

On Earth, extraction of platinum group metals from primary deposits starts with grinding the rocks. Suppose we get to skip that on the Moon. After first crushing rock the PGM content is enhanced by flotation or other gravity based methods. After that, the crushed material is smelted to produce a metallic matte that is mostly iron, nickel, copper, and sulfur. The matte undergoes controlled smelting to eliminate sulfur and concentrate the PGM into a reduced-iron solution of nickel, iron, and copper. This separate PGM-enriched phase is produced by slow cooling of the molten metal mixture, then concentrated by grinding and magnetic sorting. The enriched phase is then again treated with acid separation, smelting, and electrorefining to produce the actual PGM. If you stop after the second acid refining, the product is about 30% PGM. That's ALL platinum group metals; if you want rhodium alone you'll need to complete the separation. If you want to skip that second acid refining stage, the total PGM content of the enriched matte is only about 0.1%. If you want to skip crushing on the Moon altogether, you only get about a 10x enrichment of PGM from regolith. Supposing you find regolith with a generous 200 PPM PGM content, that means your concentrate will only be about 0.02% PGM.

Can you afford to ship a ton of iron, nickel, and copper to earth for every kilogram of platinum group metals? Because that's what you get if you insist on no crushers. I suppose you can try to develop an alternative process flow more suited to the lunar environment, but that piles on the up-front costs before you can even think of making a profit...

Also, the acids that are turned into salts need to be recycled on-site back into acids. On Earth you can build specialized acid plants instead of reclaiming acids from low-quality waste mixtures, but not so on the moon.

Alluvial deposits of PGM can be concentrated much more simply, but they don't exist on the Moon.

Getting back to 3He reactors, they aren't quite as clean as frequently billed, because they're really 3He + D reactors. And at the temperatures needed to make the 3He + D reaction go, there's also a bit of D + D going on. And that isn't aneutronic.

Anyway, given that even the much easier D + T reaction doesn't look like it's going to be lighting up anybody's city anytime soon, I think it's fair to make the substitution

Really? Engineering imagination is all very well (I say this as someone who's designed a number of things looking nothing like the current art, but which work and make money as we speak), but it must be combined with gimlet-eyed regard for facts and rigorous discipline. tp1024 has it bang on when he says it could be done cheaper on Earth - that's an entirely valid reason for parking servers there. If doing things that cost more were a valid model, pets.com would still be in business. Here's another reason to keep servers on Earth: light speed round-trip time to the Moon and back is about 2.25 seconds. Many of Google's services depend on latencies a tenth of that time, and they even place servers on every continent partly to speed up responses - how do you solve that problem? How about sheer bandwidth? Google's entire bandwidth is measured in tens of terabits at least, but lasers can only modulate gigabits at best (without accounting for time skew due to atmospheric twinkling), so you need tens of thousands of laser receivers on the Moon - but laser beams from Earth spread to kilometers wide at the Moon, so you'd need to coat the Moon with receivers to catch individual beams.

And, by the way, Google has _millions_ of servers. Do please keep up.

I get tired of "all you need to do" wank-fantasies pimped as serious engineering proposals. "All you need is Helium-3 to save the Earth!" "Imagine a Beowulf cluster of these!" Blah, blah, blah, blah. Yammering in this vein is the sign of not enough learning and not enough practice in the field. As Steve Jobs says: "Real artists ship". It's the more polite version of "Money talks, bullshit walks".

Let me close with a parable. Jimmy Smith, jazz organist extraordinaire, was playing a gig one night when he heard a guy mouthing off about "those pedals are just for show, he doesn't use them". Smith got pissed, called the guy out, and told him: "Put your hands on the pedals, go ahead! I'll show you I'm using them. What, your hands ain't going there? Sit down, shut up, and learn something!"

As they say, in Jordan I trust, all others bring data. He was sure that he hadn't seen the thermal stuff looked at anywhere, which, could be potentially serious given that we're talking about using carbon.

Which brings me to my concern about Carbon Nanotubes, and that we might just find we can't scale them to the lengths we need. We had the same rush of interest in Ceramic Fibres when I was an undergraduate, but within a couple of years of finding we could make the 5mm fibres easily, we found that every single attempt to get them longer was failing. So ceramic fibres have quietly moved away.

As Jordan also pointed out and I tend to agree, the smaller scale designs with something you could launch with a Heavy Lift vehicle in a couple of launches might not give you a sufficient mass in GEO to "hook" to. I think Clarke might have had the need for a bloody great rock correct, and I think he might end up being bang on with the timescale.

I asked this question on Bad Astronomy board. The responder actually understood the futility of putting offensive weapons in the Moon; his answer was "command and control base, far enough from the main hostilities to survive a nuclear first strike". But above objection stands -- such manned base would take a decade or more to build, which gives more than enough tme to develop unmanned countermeasures."

Even easier - attack when the Moon is on the other side of Earth. That's a twelve hour window every day.

Which brings me to my concern about Carbon Nanotubes, and that we might just find we can't scale them to the lengths we need.

I keep reading that they are getting a lot longer in the lab, but they certainly don't have the theoretical strength yet and then they still have to be made into the strand. Maybe they will only be useful for more prosaic items, like tennis rackets. *sigh*.

"Mine-crazy Space Cadets would do much better to look at asteroids, but for some reason those have gone out of fashion."

They were never really in fashion, save perhaps for Heinlein and other Golden Age SF authors. Only recently have missions been sent to the smaller bodies, decades after probes to Mars, Venus, and even the outer planets.

There's now a minor wave of interest in asteroids because the delta-V needed to reach some of them is conveniently lower in many cases than required to rendezvous with the Moon or Mars:

This means manned missions to the asteroids are energetically more possible than going to the larger bodies. Moreover, the tiny escape velocity makes mining on asteroids a much more reasonable proposition than on the Moon, with implications for large space-borne structures such as solar power satellites.

I also think there are some huge practical advantages to testing out long(ish) duration systems and techniques on Asteroids where the trip is measured in months rather than years AND you can have several Abort to Earth options.

Some Asteroid rendezvous, landing and return trips would make an extremely logical next step, and it would be nice to get some pictures of people looking back at the whole Earth-Moon system rather than just the Earth.

Firstly I specifically did not suggest that we put Google servers that deliver data on the moon. I said the servers on the moon would be crunching data and the useful results sent back to the based earth based servers. There is no latency issue involved. There are a lot of very hard data mining problems that are computationally heavy, but result in few solutions. We are just getting into the "big data" era, and while I am skeptical of some of the claims for data mining, it is pretty clear that a lot of people are jumping on this bandwagon.

So Google has 1m servers, generating a mere $20K per server. So shoot me.

This was the intro:

A way out, probably non-economic (but who knows) idea for using the moon.

In the end, the only things that we can find in space for sure, is the experience of going there, of having been there and of trying to go there.

There's no telling if there is any use in that experience. But what is the use of the experience of writing a symphony, having written a symphony or listening to a symphony, other than the value of the experience itself? Or what is the use of climbing Mt. Everest? What was the reason?

If I remember that correctly, that's what Charlie was getting at in Accelerando or the Festival of Fools (aka Singularity Sky). The only thing that the vile offspring or the Festival were interested in, was new information, new experiences.

Currently, there is no material reason to go to space. There is just the experience to be gained by changing our perspective. Navigation, espionage and weather satellites do that. Space probes do that. Flying to Mars would do that.

It takes some intellectual honesty to not try to find excuses. It's not a material proposition. If we should ever do it, it's because we can and it's because we want to. And the only things left may be a pile of scrap metal and a flag pole. And the experience of having done it.

heteromeles @ 45 A few specks of dust on the lens of a war laser will lead to catastrophic destruction of the machine. Even if they could be kept clean in normal circumstances surely it would be easy to make a device to kick up dust over vast areas. A burrowing machine that mechanically throws up dust or blows out gas. If nobody has thought of this before can I name it? The Dust Mole.

alexandertolley @ 74 AFAIK many heavy metal ores are concentrated in the first place by jiggling the slurry of ore and water so the densest bits settle to the bottom. Obviously trying to do this in a place with little water or gravity makes things difficult.

"Most often the native platinum is found in secondary deposits; platinum is combined with the other platinum group metals in alluvial deposits." That is, on Earth we don't tend to find platinums in the location the meteor landed, they have moved and collected together because of their relatively high density. I quote Wikipedia because it agrees with what I learnt at school.

@ 75 Do we know anything about the shear strength of carbon tubes? Most of the length of the cable would have to be free of extra weight from stuff like positional adjustment thrusters because the tensile strength will only just be enough to carry itself. It will wobble and twist and waggle. The repair of junk and radiation damage would be constant like reforging the metal struts of a thousand km of Forth Bridge. You would need an army of nanoknitters that could find the damage and repair any size or shape of hole.

How would you decommission an old elevator, assuming your civilisation knows it is devolving?

I liked the space rail transport too (it's akin to the Beamrider Network from Orion's Arm and wherever they got the idea). If you're really clever, you can build the ship at the other end by shooting supply modules at it.

The problem with a 4000 km railgun is a) aiming the beast, and b) keeping the rail from flexing in any of three or four dimensions. And as Dave O'Neill pointed out above, keeping the rail warping when one part is in the sun and one in the shade will be, um, interesting.

In other words, it suffers from the same problem as the laser sail that Forward proposed in Rocheworld. It's really sad that Dr. Forward passed away, because personally I'd love it if he wrote a story where the space engine could be steered and aimed easily.

Currently, there is no material reason to go to space. There is just the experience to be gained by changing our perspective. Navigation, espionage and weather satellites do that. Space probes do that. Flying to Mars would do that.

Why do you exclude "Navigation, espionage and weather satellites" as having material benefits?

"You could accelerate a rocket in one of those to 2-4 km/s and send them up on the side of a mountain. The top end would be sealed by a rubber membrane to keep the vacuum inside the tube, but allow the rocket to crash through it without being damaged."

Wouldn't the re-entry to atmosphere from the vacuum in the tube be like hitting a brick wall even if you end at Everest's summit with a third of sea level air pressure? I am genuinely interested if anyone who knows about these things could tell me. I thought the re-entry from space was only so easy because the atmosphere increases in density very gradually with lowering altitude and can be entered at an angle to the gradient of increase.

People cite "getting off this rock for the survivability of the human race" as a compelling reason for space colonization, but that's not feasible for probably hundreds of years to come.

Today it takes thousands of earth-based engineers, millions of tons of equipment, and billions of dollars to make spacecraft parts and space ice cream. And it takes fifty times that to provide THEM with the support they need to live.

There's not even a hint of an idea how that could ever work in a self-reliant way from space.

We'd have to put in 200 years of development here on the ground before we could even begin to think about it seriously, so dreams of having a moon colony by 20x0 are foolish.

Of course no mention of Robert Forward's ideas would be complete without talking about the antimatter rocket. All we need is a way to produce antihydrogen for less than the Gross World Product per femtogram and a way to store it stably for long periods of time. Then we can get truly humonguous specific impulses by sticking small bits of antihydrogen into a stream of water, and presto! relativistic pions come flying out in all directions! (Oh, and 511 million electron-volt gamma rays from the annihilation of the electron/positron pairs). But 2/3 of the pions are charged, so a nice intense magnetic field will steer those towards the back of the rocket, resulting in thrust against the magnet coils. The other 1/3 are neutral pions, which will just plow into any old thing that happens to be in the way, including the crew quarters.

Actually, I have a soft spot for this gadget, crazy as it sounds. Must be the 12-year-old pyromaniac in me. And it is the only propulsion system I've heard of which could fit into a Winnebago (that's a big caravan for those on the right side of the pond) and still get to Alpha Centauri inside one human lifetime.

This project had its projectiles going 3.6 km/s all the way through the lower atmosphere up to 180km. As far as I remember there was another project to do the same using a rail gun and about twice the speed. So, it seems to be possible.

Why use a maglev train? G-forces of much less than 10,000g are certainly a desirable goal and so are somewhat heavier payloads. Plus, the Chinese are trying to develop something like that for passenger use (just 300m/s though) ... so, in a decade or two the technology might not even be all that new and the Chinese could certainly find a site to build it ... (forget about NASA)

While the total mass of the elevator is huge, the base is the thinnest part as it has to support the least weight.

Edwards 2002 book has the basic version base designed like scotch tape with a 2 cm width. Add as many as you like for higher loads.

Even if there were a lot of tapes made into 1 combined one (not the best design) I would expect one way to cover decommissioning is to have some sort of connector at the base that could separate on command. Worst case a steel connector that could be cut with a hacksaw?

They might be upset to lose their communications satellites, GPS, moon colonies and O'Neill habitats, all possible from a much lower level of technology than a space elevator.

I had in mind pre-space age when you said "devolving". If there are O'Neill's and moon bases, they might care about a large untethered structure in their space. Maybe they would claim it as salvage and re-purpose it :)

Are we talking at x-purposes? I thought you were talking about a civilization that had reached a pinnacle with space elevators, then was falling back to a pre-space age culture, perhaps after a global catastrophe.

That civilization might be unable to use much of the high tech still extant and would still need to be protected with fail safes. This was the scenario with long term storage of radioactive waste - how to keep any civilization safe from contamination. The space elevator would be one of those achievements that might need to be made fail safe in case it "fell down". A worst case might be some indication that it should be separated from its base, and that would have to be accomplished with potentially very limited tools.

I'd think you'd already have certain measures in place in case the elevator line failed while it was in use. At a certain point along the line, a "car" that gets dropped will go into an elliptical orbit about the earth, not go through reentry. You'd probably plant a demo charge at the point, so that if the line broke above that point, cars above that point won't be dragged down into the atmo by the rest of the structure. Cars below that point might have engines that would allow them a powered abort to orbit in the case of failure. (Drop off the unused fuel before going back down, use it for other things.) Depends on how much you value life vs. money. I haven't done the math, but I'm fairly sure the unpowered abort to orbit point is high enough up that it wouldn't have a lot of drag from the atmo.

If you blew the line at that point, you'd unbalance the main section of the elevator, but it should go into an tidally stablized elliptical orbit, not hit escape velocity. If you can't adjust the orbit, it'll play merry hell with anything in GSO. Need engines to circularize the main section's orbit, then you should be okay. (With a decaying society, might worry about satellites not in GSO or LEO colliding with the elevator. No Traffic Control.) The lower segment will fall back to earth (not sure how long of a line we're talking about, again, haven't done the math), but I think you'd be okay, provided that it doesn't hit a ship or airliner. Base station should be sea-going platform - easy surface transport, can maneuver to avoid hurricanes, no population centers in case somebody drops a wrench, so it won't be close to a built-up area anyway.

What's worth paying to put on the moon? Prisoners, assuming you have the right type of society.

The one thing that stuffing someone on the moon absolutely guarantees is that they're stuck behind a 1.2 second lightspeed delay from earth. Considering that right now stock traders try and put automated servers as physically close to the trading centers as possible to minimize delay, it's easy to imagine circumstances where an enforced second of lag would be a significant economic penalty to the prisoner...or defense for people on the ground.

As I'll explain in detail later, space exploitation and colonization are likely to happen, but MUCH LATER. It took centuries for those to become workable across the oceans, and there's no reason to believe it'll be different in space.

I'm afraid you asked the wrong question, of course. The right question is, will there be some willing to live with reduced conveniences and margins for survival, and if others are likely to be willing to cover their travel expenses, for whatever reason. History says clearly that both are true. Of course, it might same a little strange to the comfortable readers of the thread. But, refugees see the world differently; whether they're fleeing from political or racial oppression or starvation, they ARE happy to be given that chance; others like to migrate for the better chance of land, being aristocrats, or just like borders, like libertarians. On the payer end will be no shortage of institutions, from churches to colonial societies to governments to, especially, companies wanting employees. Of course, serious colonization isn't particularly imminent; trip costs are still too high.

Space's development as a frontier is likely to be very slow - just as it was for the ocean. A century passed between the first exploration by the newly invented caravel and sizeable colonization and trade expeditions. As I see it, we're early in the frontier of space - still in the exploration phase; the best historical analogy to sea exploration places us, I think, somewhere toward the end of Prince Henry the Navigator's lifetime. Henry patronized the invention of a new kind of exploration ship, the caravel, from a local kind of fishing vessel, not unlike how American and Soviets converted war rockets to space vessels for early exporation. The caravel was well-suited for traveling heavy ocean swells, and quickly. Henry the Navigator also ordered the exploration and exploitation of close and easy subjects like the Canary Islands and much of the African coast. Technological progress is far faster today, but, on the other hand, the problems to be overcome are also far steeper.

Governments and major institutions played the biggest role for the first centuries. Private industry has no real sane bizplan for exploration or exploration ship D beyond contracting. Some early, Elizabethan-era British explorations had a private angle, but except for twoish that got lucky and struck Spanish treasure fleets, all went bankrupt. And, most investors in North American colonies lost money, because they took decades for them to generate economic return and the investors thought they'd work far faster. Private ship development and fleets were quite late in the game.

It took a century, until Philip II of Spain, for an ocean vessel to be both needed and invented, good at carrying freight, colonists, and soldiers. We aren't there yet. Only after galleon use was well established could commercial ventures even be practical.

Unlike across oceans, of course, instead of technologically and biowarfare inferior natives easy to exploit, enslave, or ethnically cleanse, there's nobody for a long way out at least. In fact, Hawking's rightly pointed that the tech-inferior shoe's likely to be on the human foot once we do leave the solar system.

That also means we'll have to make and work all the equivalents of gold and silver mines ourselves, or, likelier with our own robots. That makes this a much more expensive.

The North American colonies also are worth looking on as models to improve on. From early stages, most had extensive civil rights, including voting for lower houses in a legislature. Future colonies, especially ones settled by democracies should also include contemporary civil rights and checks and balances.

Some technologies that are real possibilities that'd eventually radically improve space costs include, in order, space elevators, nanotech, fusion drives, and wormhole travel. Plenty to most of those won't happen, but any of those would improve things as galleons and ocean liners did. Of course, those that do happen are likely to be as time-consuming a challenge as galleons, clippers, or ocean liners were for us.

After reading the multiple posts over the last few weeks I could draw several conclusions about the universe I find myself in:

The rules of universe that we live in fail to provide:
a: lightweight high energy sources to be tapped for power
(antimatter being highest compact energy source?)
b: a means of high-speed low-energy travel in space
(must we always throw X out the back for Y speed?)
c: a means of short-cutting vast interstellar distances
(distance limits locking us within local domain walls)
d: freedom from thought patterns limiting us to short term pursuits
(incapable of thinking multi-generational)
e: means of escaping deep gravity wells for shiny apples
(or even shiny enough apples to go for)
f: aliens for us to marvel and say wow we could do that to
(if we're the only ones the bar must be too steep)

.... OR on the contrary instead of a limiting universe we could instead be missing some fundamental physics/changes:
a: be in a peculiar era where we only think we have uncovered the universes physical processes
(recall early 1900's before quantum mechanics..)
b: Mach Effect? maybe we've just missed some physics..
(http://nextbigfuture.com/2009/09/mach-effect-part-ii.html)
c: Short-cuts: There's still unanswered physics out there, but enough BIG ones? (dark energy/matter, cosmic accel, etc.)
(spinning black holes, pocket universes, etc..)
d: limited thought patterns stem from a short timers viewpoint... if life-extension or AI take over this could change
e: gravity well costs versus need to get out of the well: Everything we do now is predicated on repeatedly climbing the well and coming back (except robotics). If we can get past that the cost drops.
(engineered bio mining of moon/asteroids combined with robotic returns: Thinking biology designed to concentrate minerals, sheltered by robotics)
f: No aliens? Lack of imagination and plenty of time to sit around wondering why they are missing.
(we can't be the first -- Copernican principle)
(if no one else did it, we cannot -- see above)
(we cannot be near the start of a vast civilization -- the odds are against it that we're born near the start!)

I do not know which of all these scenarios is valid. Perhaps we are like those in the early 1900's bemoaning the "End of Physics" and what is left is merely mopping up the details. However, we might also have already identified the salient physics of our universe and be doomed to sit here on our rock till we cease to be players.
I do know that what you cannot imagine now can come along and change everything... We are all like sci-fi authors trying to extrapolate out our future. Do we have big "Black Swans" left in our future? (postive ones, I'm sure we have plenty of negative ones). http://en.wikipedia.org/wiki/Black_swan_theory
If we don't then the negativity shown in these forum posts is quite justified..
We've explored some of the solution space the physics of our universe limits us to, however we still have some unknowns out there. Its just not clear that they uncover enough to change the game we've been envisioning.

I think we have been showing a lack of creativity in responding to this post. If the right Black Swan Event comes along we end up looking like those who said man would never fly.

So let me end on a nano-tech twist with the much more recent headlines of "Synthetic Life" (craig venter)http://en.wikipedia.org/wiki/Synthetic_life
and suppose that we master synthetic organisms designed to extract minerals into more concentrated forms (waste). This synth life can live in low O2 concentrations, thrive in highly radioactive environs, live in cold/hot conditions, and can hibernate or be stored as spores. Now take this on robotic missions to the asteroids, stick them in inflated ballons with raw ore and let them eat. Setup a chain of robots to cycle this material to LEO for heat shield based drops to earth.

All of the features I've mentioned in the synth life exist in earthly forms, its just a matter of getting the right genes together. There's no big machinery, just small robots and solar sails. This picture of mining is much more sustainable than the processes from the movie "Moon" were. This is what I mean by a dearth of imagination... make it a bottoms up mining operation, Not a macro one with humans manning the "pickaxe".

@ 16
"When do we get AI?
When computers stop being serial, and become massively "parallel" or better still multiply internally interconnected - each computing chiplet is connected to its 14 nearest neighbours (assuming cubical shapes)
See also my last comment at the bottom.

Charlie @38

@41
Space elevators need stronger. more reliable materials.
But we're getting there.
I would guess it will be feasible in the next 50 years.

Obligatory reading: "Arms and the man" by (I forget), a biography of Gerald Bull (who ran Project HAARP). His martlets were actually two-stage solid fuel rockets launched using a discarding-sabot system from a massively hacked ex-naval 16" gun. The Iraq Supergun was going to be the next step in his plan to deliver cheap unmanned access to space via rocket-boosted artillery, until Mossad intervened (probably because he was funding it with political capital realized by designing workable RVs for Saddam Hussein's IRBM program).

It's interesting to speculate on how things might have turned out if Bull had found a less controversial sponsor.

The cynical thought just occurred to me that there might be no way of having non-controversial cheap access to space- the countries that can pay to do it now probably benefit from having the high ground.

Since "They can put things into orbit" means "They can drop bombs on my cities", and if they can do it cheaply...

Another problem with cheap space tourism: if you think 9/11 was bad, contemplate the prospects for what a group like the Hamburg Cell could have done with an orbit-capable reusable winged people-carrier with cross-range -- or even a sub-orbital one like the Virgin Galactic toy. Then contemplate the security that'll be needed around such craft.

I don't think it's sunk in yet, but any craft capable of delivering tourists that genuine zero-gee ten minute ride is functionally close-to-indistinguishable from an IRBM launch stage.

A really sturdy cockpit door would be fine for that scenario. Or a self-destruct button in easy reach on the control panel and pilot with a deep feeling about the greater good.

Private spacecraft, but government or quasi-governmental pilots, maybe? So you can own the ship, and you can plot an approved course, but you can't actually get your hands on the steering wheel to deliver a...let's see, earth to moon delta V is 14-15km/s...package.

Carbon nanotubes are probably stronger than you'd think. I used to work for a place that made carbon fibre furnace insulation,goodto 3,000C in Argon (Do it in vacuum and it starts to sublime) and twice production managed to turn our largest, carbon lined furnace into a kettle full of hot water (Ok, maybe it wasn't entirely their fault) and the insulation was still usable when dried out. Not to mention the way that quenching the stuff wasn't much of an issue.
Plus carbon has a fairly low coefficient of thermal expansion.
Finally, how much can you clad the elevetator with insulation? And you have to keep the air off the carbon, since if it gets above 400C or so it will start to smoulder and then burn, which would be embarassing.

Cool! That's a failure mode for a space elevator I've never seen in fiction -- terrorists/military blowing them up, sure, but catching fire? Damn, now I need an excuse to use one in fiction ...

Depressingly, though, this may be a major obstacle to the development of orbital pinwheel/skyhooks -- if you're dipping one end of a tether into the stratosphere at each perigee pass of a highly elliptical orbit to grab payload cannisters, dumping the waste heat from that end is going to be a major problem.

Kevin @104 - re: survivability of the human race - yes quite. Also if we can build a self-sustaining colony in space we can sure as heck build one a lot easier on earth even in the aftermath of an ice-age causing asteroid. Or are we worried about the sun going nova or similar?

Jon @ 122 - I'll believe these refugees, libertarians, etc will colonize space when they've first built giant floating cities on international waters, underwater cities + biosphere type cities in the deserts, wilderness and polar regions. All far easier than getting irradiated getting Mars just to live "free". We aren't short of space on Earth, just land that's flat(ish), not short of water, politically stable and non-corrupt with a decent climate and a decent infrastructure connecting it to the rest of the world.

Markham @123 - of course someone has to be first? It's like winning the lottery - just because it's wildly improbably doesn't mean you should reject the notion even if the numbers on your ticket match the winning numbers, purely because the odds are so far against it.

C @126 - precisely. If you think nuclear proliferation is a problem wait until commercially available space-flight is widespread.

alexandertolley @ 117 Sorry, you confused me by using "pre-space age" to apply to a post-space age scenario. Which is only one of the possibilities. Post-space elevator being a very different matter.

If we are talking at cross purposes then it seems to me that it is because you are looking only at the best case scenario (the great-great grandchildren will be able to take care of that, or they won't care, haha). Failsafes would be tricky in my opinion. As soon as it starts moving I would bet that a real cable would rip itself to shreds.

Glad to see you have given up on defending the moon-mining idea.

tp1024 @ 131 Fluorinating the surface of the cable would make it a little trickier to for the climbers to get a grip. Not that I have seen any realistic designs for the junction between climber and cable.

@112 Gerald Bull's gun used rockets in a tube with atmosphere in it. Is the instantaneous change from vacuum to atmosphere so insignificant?

Greg Tingey @124 I think mineral dust actually on the lens is a little different from firing through moist, dusty sea air. The scratches from wiping the moon dust off regularly might be problematic too.

Am I the only one who would build a research lab on moon, to be able to do some bigger secret research? Seems like it would be easier to hide what you are researching without a ton of satellites aimed at you.

Fluorination wouldn't be anywhere near enough, I'd need to check what temperature it would dissociate at but I'm pretty sure the friction would be rather high. What sort of speeds are we talking about here?
You'd need a heat sink, which if we had something like in NIvens ringworld would run up the outside of the cable, dumping lots of heat into the orbital counterweight, which could be used for mineral processing or a sterling engine, which energy could then be used to run the elevator cars.

Of course attaching the cars would be fiddly as well, as others have already pointed out. HOw much do you trust magnetic or other clamps, alternatively what sort of ever turning, hhmm, I've just had an idea- how about the entire outer section of it is done like a double helix and the cars move up the gap between the two helices, thus can be protected from external issues such as the friction and there would also be space for rails for them to move on. Of course the continous sideways feeling would be weird at first, and of course the rich would use ssto craft rather than spend 2 or 3 days in a box.

If we know the cvelocity of the end of the beanstalk we can do comparisons with the space shuttle, which has some reasonably effective carbon fibre insulation protected by a relatively thin layer of oxidation resistant ceramic. But we all know what happens to the shuttle when that surface is broken. Can you imagine the kind of thriller set up you'd have with the rotation of the beanstalk meaning you have x hours before the terrorist/ accident damaged leg returns to atmosphere and you'd have a major incident on your hands? (If anyone writes this story, give me some credit for the idea)

As for lenses, I thought we had some pretty good ceramic coatings for them that were much stronger than normal rock dust and would thus easily not be scratched when you cleaned the lense. BUt I'd need to speak to my ex-boss about that, he was involved in lens coating at Barr and Stroud a few years back, various top secret projects involving submarines and aircraft.

Don't forget lightning strikes. I'm sure a conductive cable (aka a beanstalk wetted by rain) running that high will get some interesting charge differentials running up and down it. Especially since you need to place a beanstalk in the tropics.

Ben Franklin would applaud. And that doesn't even talk about what the Van Allen Belt is doing to the other end!

Maybe this will be the real use for beanstalks? Powering the world? All you need are some really, really big capacitors...

The link I provided was somebody who had done the maths, which makes instructive reading. His comments on "bad thing" for the true Ghostbusters sense of the phrase involve the energy tied up in a substance that strong.

The cars are your least problem. The real one is what's left falling on the Earth and the next XX,000 km of cable rolling out through Earth orbit.

He makes a point of saying that a cable failure would probably be fatal for any other elevators too.

I'd like to think that Carbon Nano-Tubes are strong enough if we can make them of length. But between Jordan's objections and the website I looked at, I'm feeling that there are some fairly horrific failure modes that will take a LOT of fiddling to resolve.

Fire wasn't one I'd considered, and I'm not entirely sure about how you could insulate the cable without causing serious problems with the mass and also handling the crawlers.

On the subject of crawlers *another* seemingly innocent question Jordan Kare raised was what material do you make the wheels out of (No, we are not, at this time talking maglev)... that opened a whole other can of worms - a lot of current designs are fiddling with Aluminium which doesn't quite cut the mustard.

Using nitrogen with NERVA would be brilliant, if it gives you a higher temperature exhaust somehow. Have you got a cite for that, before you dash off to WorldCon? I couldn't find much relevant on google.

I was thinking purely in terms of ease of handling and availability. (LN2 is piss-poor for Isp, but is dirt cheap and easy to get hold of.) Looks like methane might be better, mind you. In the 1950s and early 1960s the Soviets were looking at ammonia as a low molecular mass reaction mass for nuclear rockets; low molecular weight, high-ish boiling point so easy to store, and so on. But it doesn't buy you that much that's better than plain old-fashioned water.

Yes, crawler wheels...
INteresting problem. HOw hard would it be to braid carbon nanotubes and use odd spiked wheels which would have a very rough surface which settled nicely within the brains of tubing? Of course you still have to be able to make hundreds of metre long tubes though, but if you have that cracked surely you can manage near flaw free manufacture of tens of thousands of miles of braided nanotube? ;)

Then of course you need a motor capable of driving our hypothetical carbon wheels running fromwhatever power it picks up on its travels.

And I do like my idea of making the outer section of the beanstalk with a helical void for the crawlers.

In fact how about making a 200,000 mile long elevator cable and connection two cars together, one going up, the other down?
Och, this has no doubt all been covered before on usenet groups 20 years ago or something. NEver mind.

After reading the various comments on what the point would be in building a moonbase, I can only see one convincing reason: you are an Evil Criminal Genius and need something on which to spend the hundreds of billions that your secret criminal organisation generates, which this would clearly do... as well, of course, as providing a perfect Secret Base.

Of course not. I was making fun of the post at number 88. I read 88 and immediately flashed on the old joke about how one mounts an expedition to the sun without burning up - you go at night.

The poor logic in post 88 was similar. Imagine a "command and control" base on the moon. Imagine that the designers are so goddamn stupid that they don't realize that someone could launch from the opposite point on Earth from the moon and do something about it, not to mention that the distance from Earth to Moon, once one has left orbit, is something like 240,000 miles, during which the attack is easily dealt with. Also note that with anything resembling current technology, the attacker's launch cannot be "stealth" during the initial boost phase. Etc.

The association seemed so obvious to me that I didn't think I'd need to explain. (This is probably why Charlie is published and I am not.)

Here's an alternative launch option: Take something like a heavy lift balloon or a statalite (maybe NASA's ULDB project)http://www.spaceref.com/news/viewpr.html?pid=16024
Lift your payloads to the edge of space, once there various options open up:
(1) a carbon fiber tether hanging down from geosync to snag the ballon and finish the pull up
(end point hanging above earth's flight is powered by charge differential in the cable)
(no need for full extension down to earth)
(2) a space based microwave powersat beams power down to the ballon for gradual lift to orbit (say via a xenon based ION engine)
(3) space based powersat beams energy to the ULDB to heat the ballon for even greater lift. Here's where my science gets weak: the ULDB launches solar sails similar to the JAXA onehttp://www.wired.com/wiredscience/2010/06/solar-sail-deployment/
which also taps the microwave beam to gradually rise into LEO
By weak science I make several assumptions here:
(a) a ULDB altitude is great enough to allow a spin unfurl of a solar sail
(b) enough lift could be tapped to continue to LEO via use of the microwave energy

I have no idea what the maximum weight that could be lifted to LEO using such methods. But none of them require anything beyond basic engineering. There is the large initial cost of the powersats, but reoccurring costs would be low.

how to power a climber thousands of kilometres overhead economically and efficiently enough to make GTO in something less than months; how to survive transiting the Van Allen belts slowly:

If we stipulate only cargo and propellant transport all the way to GTO, while people take faster transport, thuis obviates the need for surviving the radiation belts as regards the practicality of elevator transport.

It might be possible to have rotating skyhooks rendesvous with the elevators, allowing people to ascend quickly to 100-1000 km, be picked up and whisked away to high orbits with the skyhook, reducing transit times through the Van Allen belts to acceptable periods. This is a departure from the usually suggested spaceplane ascent, but might make sense if the elevator already exists for cargo. Because the passengers are lifted above the atmosphere, neither the skyhook nor the transfer vehicle need suffer from atmospheric effects.

Can you imagine the kind of thriller set up you'd have with the rotation of the beanstalk meaning you have x hours before the terrorist/ accident damaged leg returns to atmosphere and you'd have a major incident on your hands? (If anyone writes this story, give me some credit for the idea)

Kim Stanley Robinson got there first. His Mars elevator was brought down by "terrorists" and nicely wrapped itself around the planet.

I was thinking purely in terms of ease of handling and availability. (LN2 is piss-poor for Isp, but is dirt cheap and easy to get hold of.) Looks like methane might be better, mind you. In the 1950s and early 1960s the Soviets were looking at ammonia as a low molecular mass reaction mass for nuclear rockets; low molecular weight, high-ish boiling point so easy to store, and so on. But it doesn't buy you that much that's better than plain old-fashioned water.

That one's already been done - Asimov's "The Martian Way". True, he use "proton micropiles" to heat water instead of a reactor but practically speaking there's no difference since it was just the sort of transfer mechanism used in NERVA. Since the little miracle worker wasn't an "He-3 micropile", I'm guess there were some radiation issues as well.

Although iirc, heating water up to 3,000 degrees Celsius doesn't do your piping any good; nitrogen isn't quite as reactive as oxygen at those temperatures.

I was wondering about argon as a propellant for a NERVA kettle engine -- as a noble element it doesn't react easily if at all so there's no worries about corrosion or chemical combination in the exhaust. It's heavy (molecular weight of 40) so reduced exhaust gas velocities due to friction in the reactor tubing etc. will still result in a decent amount of thrust, and it's pretty cheap since it is common (nearly 1% of the atmosphere by volume). In liquid form its density is 1.4 kg/litre, a lot better than water at 1kg/litre or LN2 at 0.8kg/litre so the tankage needed to hold a given amount of reaction mass will be reduced. I note with interest that the Martian atmosphere is believed to be about 1.6% argon...

Most space-going ion engines use xenon -- I presume this is because it's a nice heavy nucleus and the cost of the xenon is not a significant factor in an otherwise gold-plated space project.

“This beanstalk isn’t here because it’s the easiest way to get people to Colonial Station, you know. It’s here because it’s one of the most difficult— in fact, the most expensive, most technologically complex and most politically intimidating way to do it. Its very presence is a reminder that the CU is literally light-years ahead of anything humans can do here.”

you need to know the difference between thermal engines and electric engines. The energy that NERVA can put into a molecule or atom is limited by its operating temperature which is less than 3000K, period. Otherwise the reactor melts or gets vaporized. The heavier the atom, the worse efficiency gets and it gets real bad real fast. And argon is in real-bad-territory.

Ion engines are different. They don't heat up a gas, but directly accelerate ions into a given direction (heating up a gas results in ions/atoms to be accelerated in *all* directions). The energy per ion is no longer limited by operating temperature, but voltages and those can be cranked up pretty high. That's why argon is quite popular there, as it has the benefit of being relatively easy to ionize and chemically inert.

Plasma engines (like VASIMR) also heat up a gas (or rather plasma) and are constrained by achieved temperatures. But those can be much higher than in NERVA, as the plasma doesn't touch the plasma chamber. Lighter fuels (they tried deuterium for some reason) are more efficient, but temperatures are so high that even argon is good enough to deliver great efficiency.

Another option to get to LEO:
Take the ULDB concept from my previous post and use that as a launching platform for payloads powered by electrodynamic tether. Basically drop a few kilometers of wire down and use the power generated for your Xenon engine or even "surf" the Lorentz force. I know you can drop altitude but what about raising altitude?
I like the idea of powering a ION engine up with tether generated power.

In The High Frontier, Redux, you argue interplanetary travel is too hard. Much of your argument rests on the difficulty of lifting stuff from the bottom of earth's gravity well.

Well, lunar water isn't at the bottom of earth's gravity well. It's 2.5 km/sec from EML1. With the use of aerobraking drag passes, it's about 3 km/sec from LEO. That's water for drinking as well as radiation shielding. Oxygen to breathe.

Most importantly, fuel and oxidizer for rocket propellent. Lunar hydrogen and oxygen exported to LEO propellent depots could be a huge game changer.

As it now stands, getting past LEO takes delta V budgets 14 km/sec or greater. Sources of propellent at different orbital locations could enable travel between these locations with 4 to 5 km/sec delta V budgets.

Further, the moon's 2.7 second round trip light lag might allow mining lunar water with telerobots. You yourself mentioned the possibility of lunar telerobots in The High Frontier Redux. John Atkeson's comment #215 on Space Cadets outlines a possible path towards improved telepresence. Given that Moore's Law is still holding, I don't regard this as implausible.

If we can mine and export lunar water roboticly, that demolishes one of the fundamental assumptions in The High Frontier, Redux.

Apparently there's a Wiki article on "Tether Propulsion". I suppose instead of tapping the electrodynamic power for an active propulsion device you could just do this from the balloon:http://en.wikipedia.org/wiki/Tether_propulsion

Why would the efficiency of the NERVA go down with a heavy molecule like argon, and would it actually matter?

Feeding a NERVA engine with a non-noble gas produces a stream of very fast-moving very hot gas which react chemically against the white-hot tubing it is flowing through. That will strip and erode the tubing quite quickly, reducing the burn time before repair or disposal of the engine is required. To reduce those effects the temperature and/or the flowrate need to be reduced resulting in lower thrust, something that could be counterbalanced by using a heavier molecule.

Liquid hydrogen is bulky so it needs large tanks which add parasitic weight to the spacecraft and it also needs good insulation as it boils at very low temperatures so long-endurance missions would be more expensive mass-wise if stored reaction mass was needed at the other end of the trip to slow down again. There is also the problem that hydrogen is light so you need to throw a lot of it through the reactor to get a decent amount of thrust.

A high-molecular-weight reactant such as argon would require less tankage than hydrogen or other common liquid reactants and as a noble gas it can be flowed through a reactor core without causing chemical degradation of the tubing. Liquid argon is denser than H2O, LN2 or even LOX so the tankage overheads can be substantially reduced. The lower exhaust velocity is compensated for in part by the higher mass of the exhaust gas stream -- it's not a total substitution for the V-squared KE losses but it makes the engine more practical to build, maintain and operate.

Because of the rocket equation. To get to LEO, you need a delta v of roughly 9km/s. (That includes losses due to friction, gravity etc.)

Using hydrogen, your exhaust velocity is about 9km/s. Using argon, you're down to 2km/s.

In order to get a 100t space ship (including payload, tankage, structure, heat-shield and the nuclear reactor) into orbit with a single stage, you will need either 171 tons of hydrogen or 8650 tons of argon.

I'm not sure it follows that suborbital launch vehicles are a completely game-changing technology in the homeland security field. Something the size of SpaceShipTwo crashing into a building would cause significantly less damage than a fully fuel-loaded 747. (And it would be harder to go to piloting school to learn how to pilot after you'd hijacked).

The reason IRBMs are so scary is because they typically carry a nuclear warhead, and if scary terrorist types get their hands on one of those, I think of plenty of truly horrifying scenarios involving delivery, without having to go through a Hollywood movie-style plot involving hijacking a space tourist flight.

Something the size of SpaceShipTwo crashing into a building would cause significantly less damage than a fully fuel-loaded 747.

Depends how fast it's going. Remember Newton's laws of motion? Kinetic energy scales as the square of velocity, and a sub-orbital ship is going lots faster than a 747. (Mind you, 747s are so honking huge that, with a hundred tons of fuel on board, they'd make a real mess of anything they hit; you'd need a non-tiny sub-orbital ship to compare.)

POst #165 bringing us back to Heinlein, and how in Friday, she points out that brains in a vat as pilots for suborbitals might be a problem because they couldn't be relied upon to care about humans or human problems enough to avoid causing some sort of trouble.

Well, the guy in your link does know more than I do. However, I think the thread failure thing is more about normal wear-and-tear than a catastrophic failure. Apparently, under these kinds of tension, a nanotube thread has about the same energy density as the same mass of TNT, so the failure of a single thread will do some considerable damage to the surrounding cable.

According to this guy, it looks like the unpowered abort-to-orbit point has an orbital altitude of 23.4 thousand klicks. (I'm think this above surface, not from the Earth's surface, right?) Place a demo charge at that point, and anything above that point won't hit atmo. (At least not until the orbit decays from atmo drag - I somehow forgot that this would be an elliptical, atmo-grazing orbit.) Anything below this point will re-enter, and will scatter over 129.5 degrees of longitude. However, this is ignoring that most of the higher altitude stuff will burn up instead of impact. Also, only they highest 5000 km will fall more that 45 degrees of longitude from the anchor, and there are places where you have 45 degrees worth of ocean.

He does have a point that debris from one failed elevator will do very bad things to any other elevators. However, given how messy Earth orbit is already getting, I would hope that an elevator would have active anti-collision defenses. Granted, a failed elevator might overload those defenses...

A catastrophic elevator failure might actually be pretty survivable. Any climber above the unpowered abort-to-orbit point should be okay (assuming they don't get taken out by cable whiplash or debris). Climbers below the UATOP might be able to make a *powered* abort to orbit, or make a safe-ish splashdown in the ocean. Main thing you need to do is to circularize the main station up in GSO, or it will eventually take out everything in GSO. Which would be bad. This might require cutting off the higher bits of the tether, and replacing them when things have settled down. (This will pretty much screw any climbers on those parts of the tether, since they will be taking an unplanned interplanetary expedition.) Also, have orbital stations in LEO to send rescue ships to stranded climbers that aborted to orbit before their life support runs out or their orbit decays. Same thing from the GSO station.

As for transversing the Van Allen belts, how about this: Manned climbers jump off the elevator just before they reach the belt, then use a Hohmann transfer to re-rendevous with the elevator above the belt? (NB: the UATOP is *above* the inner belt, would probably make a good "landing strip." GSO is above the outer belt.) How much delta-V would this cost? How long would the crew be stuck in the belt?

Yes, velocity is squared, but energy transfer is the important part. If something small and light is moving really fast, it's going to go right through a building, whereas something that's big, slow, (and full of fuel for an inside straight) will stick in the building (and explode). It's the difference between what a meteorite and an automobile do to a house, assuming they hit with the same energy. The car punches a much bigger, messier hole, and then you've got to remove the projectile, too.

You only get limited energy transfer if you hit a narrow target going horizontally (or nearly so). If you hit a high-value target (the White House, London Stock Exchange, Mecca, whatever floats your boat) either just above ground level or going as near-vertically as you can arrange from your orbital profile, you're going to transfer all your KE in a really good ground-shaking impact.

Um, if you think Charlie might have a point about governments getting worried by the possibility of people hijacking spaceplanes, wait till you see how they react to the idea of putting multiple kilo-tonne lumps of stuff into unstable LEOs and then bouncing things off them. Sure, your moon-ice 'refueling station' is going to be rather harder for potential hijackers to aim - but there are people to whom that won't matter (there are targets big enough to be really easy to hit - the EU, India, China, Brazil, the USA...).

I can't see governments responding well to privately funded colonization programs, either, come to that. "You want to assemble how many thousand tonnes overhead, with an inertial guidance system attached?"

Just for the sake of curiosity (and there will be a good reason it won't work I am sure) but wouldn't the moon be a good place for continuing to look out at the universe - sort of a next, next, next generation version of the Very Large Telescope (with lower gravity, less atmosphere etc).

Generally Big Budget things tend to come from either the bang bang school of funding or the head scratchers anonymous side.

A Farside Observatory is somewhat doable, but kinda runs counter to the whole space-cowboy thing. 1) It'd be a non-profit operation, probably funded by the government. 2) It wouldn't be a *colony*, but pretty similar to the Antarctic research bases. 3) It wouldn't be big enough to hang a private space industry infrastructure off of.

It also would be pretty expensive, and our science dollars might be better spent elsewhere. But the Farside *is* about the only place to put a radio observatory away from Earth's radio output.

I do remember the laws of motion, but I also expect that it'd be tough to hit a ground target at anything approaching 2600 mph (which Wikipedia mentions as the top speed for SpaceShipTwo). It's likely designed to hit that speed when it is above most of the atmosphere, and drag and pressure loads on the airframe will be much lower.

Coming back in on a normal trajectory will have it hitting the target at subsonic speeds. The worst-case scenario likely involves firing the passenger stage not straight up, but rather along a trajectory that goes straight into the building, and hoping the wings don't rip off along the way.

Don't get me wrong, I wouldn't want to be in a building it was pointed at, but I'm not sure it's an entirely new magnitude of threat.

How about a lunar archive for pirate movies/music/code (books having being declared old hat)?

Send a relatively small storage and transmitter payload to the near side. Payload buries itself deep in the regolith with just the transmitter dish peaking out.

Anyone with the moon above the horizon can pick up transmissions of the latest pirated movies, TV, etc. using a simple radio dish, and those with bigger dishes can upload new content. No traceable connection for downloaders except a dish on its back in the garden.

If MPAA or RIAA get round to sending a missile to bomb the site, they can be seen coming and the transmitter hides away again till the danger has passed.

Give it a decade or two and the moon becomes a safe haven for those looking to escape the stifling constrictions of corporatism on Earth.

While it would make sense to put any lunar radio observatory on the far side, optical telescopes may be another matter because of the lunar dust. The Apollo astronauts found it impossible not to get covered by the stuff and one wonders whether the optical elements could remain dust free.

The only place where water gets you anything is outside the gravity well.

No, just getting out of the atmosphere gives you an advantage, because Isp is significantly lower if the exhaust gas has to push air out of the way. By way of example the Shuttle SSME has an Isp in vacuum of 452, and in air of 363. Note that the NERVA-2 design, using liquid hydrogen, spec'ed an Isp in vacuum of 825, but at sea level only 380.

any craft capable of delivering tourists that genuine zero-gee ten minute ride is functionally close-to-indistinguishable from an IRBM launch stage.

And any craft capable of reaching orbit is effectively a FOBS, meaning that it can hit anywhere on Earth, even antipodeal from the launch site, has a peak altitude of a couple of hundred clicks instead of the 6,000 or so for an ICBM, and you can't tell what it's aimed at until it de-orbits, at which point it's about 5 minutes from target.

As for preventing hijacking, I wouldn't depend on an armored door. The best way to take control of a complex air or spacecraft is to hack the control computers. Current computer security practice within the military (US from my own knowledge and little reason to have faith in others) is rather poor, for most civilian applications outside of financial institutions it's practically non-existent. Remember the adage that the only secure computer is locked in a vault, disconnected completely from the outside world, and powered down.

Well, as other people have noted, ballistic missiles are horribly bad and ineffective weapons if you don't have nuclear, biological, or chemical weapons on top of them (which I'm guessing the unnamed user of suborbital vehicles as weapons does not, since they would presumably go with easier delivery methods than trying to hijack a sub-orbital vehicle close to their target while carrying the doubtlessly heavy and noticeable weapon on board). That doesn't mean they won't be controlled as weapons (rather than airplanes), but it's not quite so straightforward as you make it out.

See knew there would be something - dust - though guessing anti-static charging or self cleaning systems currently under development would help that ;)

Idea was to get away from the "space cadet" view and see if thre was a genuine reasonable idea that would work - scientific research along with military investment tends to take longer, non-profit (direct profit anyway) views of things (nothing stopping it being out sourced though...).

Antarctic is a good example - per annum more people visiting, more quiet investment and lots of big players shuffling uncomfortable waiting to see who moves first into a more colonial move.
May not be the wild west gold rush, more a slow evolution.

Space Cadet fantasy head back on (well a bit anyway) - personally asteroids / comets are where its at - parking one in orbit has some reasonable value when treating it as a money saving initiative, assuming the money is being ear marked for expenditure (ie we are going to transport X material, so Y solution will "save" money)

Lunar water is a potentially useful resource for getting further; unless you have a reason to do that, it's not relevant. It's nice that getting to Mars or Vesta from the moon would be easier than we thought ten years ago, but what do we do when we get there, and do we really gain by leaving Earth's gravity well, landing on the moon, and then taking off again, thus dealing with lunar gravity both when landing on the moon and when taking off?

Another reason governments might be nervous about a space elevator: in the Robinson book, the terrorists were able to bring down the space elevator because they had installed a self-destruct mechanism when it was built. Suppose you're the government of the United States. Do you like the idea of someone in Brussels, Beijing, or Brasilia putting that thing up with a self-destruct mechanism, or is it going to look safer to sabotage it before it's huge and threatening?

There's another issue with fusion power: it too causes global warming. Ditto with fission. Indeed basic blackbody thermodynamics says that if you generate more heat, the temperature of the planet must increase so as to better radiate that heat back into space. While the effect is not nearly as strong as greenhouse pollution (e.g. CO2, CH4, black carbon, N2O, etc.), it is still an effect that must be considered. Earth receives 120,000 TW of energy from the sun. Humans currently use 18 TW of power. Were we to generate any significant fraction of the 120,000 TW from non-solar means, it would create warming. If you think that is so far away, then you haven't considered the power of exponential growth. Consider the article Long-Term Global Heating From Energy Usage in the 8 July 2008 issue of EOS, from the American Geophysical Union (i.e. scientists who know this sort of thing); it included the examples,

If global nonrenewable energy use continues increasing at its current rate of about 2% annually and if all greenhouse gases are sequestered, then a 3Â°C rise will still occur in roughly 8 doubling times, or about 280 years (or ~350 years for a 10Â°C rise).

More realistically, if world population plateaus at 9 billion inhabitants by 2100, developed (Organisation for Economic Cooperation and Development, or OECD) countries increase nonrenewable energy use at 1% annually, and developing (non-OECD) countries do so at roughly 5% annually until east-west energy equity is achieved in the mid-22nd century, after which they too will continue generating more energy at 1% annually, then a 3Â°C rise will occur in about 320 years (or 10Â°C in ~450 years), even if carbon dioxide emissions end.

There are limits to growth on Earth. We are actually quite close to those limits. Civilization collapse is more likely than continued exponential growth.

"and do we really gain by leaving Earth's gravity well, landing on the moon, and then taking off again, thus dealing with lunar gravity both when landing on the moon and when taking off?"

I'm not suggesting landing a Mars vehicle on the moon to get lunar propellent.

This is the Tucson to Omaha by way of Houston argument. Someone arguing Texas gas is worthless might argue "Why drive all the way to Houston to get Texas gas?". They are ignoring the fact that Texas gas is exported to Albuquerque and Denver.

The moon is quite close to EML1 and LEO. In terms of delta V, it's much easier to export lunar propellent to these locations than from earth. A mars bound vehicle would not land on the moon to get propellent, rather stop at lunar supplied propellent depots at LEO and EML1.

Can it really be said to be a better method of hijacking, when nobody's done it yet? (That one episode of The Lone Gunmen doesn't count.) I can't believe it would be any easier than bribing/blackmailing for a means of physical access. Besides, by remote-controlling a rocket into a building, you don't get that lovely frisson that spectacular suicide gets you.

I wonder if the "if you mine the Moon very bad things will happen" idea didn't come from the '70s TV classic The Six Million Dollar Man. In the two part episode "The Dark Side of the Moon" a renegade scientist who is supposed to be on an asteroid mining mission is actually on the Moon trying to mine a new material he thinks will be a cheap source of energy. But his activities are effecting the Moon's orbit, resulting in various problems back on Earth.

I'm not suggesting landing a Mars vehicle on the moon to get lunar propellent.

This is the Tucson to Omaha by way of Houston argument. Someone arguing Texas gas is worthless might argue "Why drive all the way to Houston to get Texas gas?". They are ignoring the fact that Texas gas is exported to Albuquerque and Denver.

This can't be said often enough: propellant is not the main cost driver for rockets.

Let me go back to my favorite example for this sort of thing, the rockets in "The Martian Way" where a propellant is heated by an external source. Now, the performance of those rockets weren't any better than what you're going to get with a NERVA-type setup. Nevertheless, they are far superior to anything we can build today in terms of the most important factor: maintenance and manpower. Asimov's rockets - as were a lot of those back in the day - could be successfully operated and maintained by what are by today's standards a vanishingly small number of people. Sure, they have specialized knowledge and specialized tools, but at the end of the day Dan Kirby, rock jack, can do 90% of the work on his personal machine all by himself.

That's where the money is to be saved. Not in fancy propellant schemes.

Thanks for the numbers making clear that there's no point in NERVA unless you use hydrogen or helium as the reaction mass.There's another problem with NERVA for SSTO - they're high in specific impluse, but SSTO also needs high thrust-to-weight ratio to get anywhere with excessive gravity losses.

Nuclear thermal rockets have crap thrust-to-weight, I think due to low density fuel, thus large tankage, large engine internal area for heat transfer, and the heat exchangers having to be built like bricks coz you're trying to squeeze turbulent hydrogen through them at 3000K.

I was thinking of alternative reaction mass choices for free-space NERVA flights (LEO to Mars orbit, perhaps) rather than SSTO from Earth. I get the impression a hydrogen-fuelled SSTO NERVA is pretty much scrap metal after a single launch given the hammering its reactor core will take during the burn, disregarding the problems of licencing the operation of such a motor in Earth's atmosphere.

My idea of using a high-molecular-weight noble gas propellant such as argon was that running it through a space-based NERVA reactor would cause a lot less damage to the core, in part because there would be no chemical reaction to strip metal away and throw it out the exhaust and the higher molecular weight and density would compensate somewhat for the lower exhaust velocity. This is a big engineering win for a shuttle vehicle flying back and forward between two celestial bodies on a regular basis assuming it can be refuelled at either end of the trip.

I thought for a time that the Saturn V first stage was fully-cryogenic until I read up on it and discovered that the RP-1/LOX mix used was actually necessary to get it off the pad as a LH2/LOX motor and its resulting tankage couldn't meet the first-stage thrust requirements due to the low mass of the resulting exhaust jet. The Shuttle is effectively a single-stage vehicle burning LOX/LH2 but it requires the SSRBs to provide 80% of the takeoff thrust and it "cheats" in a number of other ways.

Well, no, but since you only have so many suicide attackers, by hacking the guidance systems you could theoretically put _all_ the planes in the air into buildings rather than just a few. Frisson indeed.

You really need to use a low-atomic weight propellant, otherwise your specific impulse is dire. The specific impluse from using helium is pretty close to that of hydrogen without the material problems that come with hydrogen. Argon just loses you efficiency with no other gain over helium.

It takes ~10 km/sec to get from earth's surface to LEO. Then on the return trip, the ship suffers a lot of abuse when 8 km/sec is shed within an hour via aerobraking. It is possible that such vehicles will always be multi-stage expendables. (Although at the moment I'm giving Skylon even odds.)

Vehicles between orbital destinations are another story. A ship designed for round trips between EML1 and LEO could have a delta V budget of ~5 km/sec. Same is true of lunar ascent/lander vehicles that travel between the lunar surface and EML1.

Ships that suffer no re-entry abuse and have low delta V budgets can be smaller, single stage reusables. This makes a huge difference.

Propellent to dry mass ratio delivered to destination is e^(dV/Ve) - 1. Where delta V is your delta V budget and Ve is your exhaust velocity (typically in the neighborhood of 4 km/sec for chemical propellents). You can see that as delta V goes up, your propellent mass goes up exponentially. Now some of the dry mass must be rocket engines, tanks to hold propellent, power source, etc. Shrinking the dry mass to infinitesmal fractions is impossible. That is why big delta V budgets mandate multi-stage expendables.

The object of multiple propellent sources isn't to save propellent.

It is to break the exponent in the rocket equation into smaller chunks. If an 18 km/sec trip could be broken into smaller hops of say, 4 to 5 km/sec per leg, the trip can be accomplished with smaller, simpler, reusable vehicles.

It would still take lots of propellent. But, as you say, cost of propellent isn't the main cost driver.

Keeping Helium liquid compared to Argon is a problem. As others have mentioned, there are issues of the tank sizes and cost that will change the performance equation. There is also the issue of refueling. Hydrogen from asteroid water is going to be a lot cheaper and more available than Helium from earth, once a space infrastructure starts to be put in place.

The space elevator principle gets you to Geostationary, slowly. ( Once the thing has been built )

Seriously, what's wrong with using airships/balloons to get above the thickest part of the atmosphere, before firing up whatever your main engines are?
Or eve have 3 sets of motors (weight penalty, I know) - ducted fans for take-off, then jets to really upper atmosphere ( approx 20k up ) THEN rockets ....
Or even just the last two.
Wasn't HOTOL something like the latter?

As an ICBM platform the lunar nearside sucks -- anyone can see you coming as soon as you launch, days in advance. Farside is more practical, but is vulnerable to pop-up first strikes coming over a horizon that is much closer than it is on earth, hence there's less warning time.

That's a good thing, not a drawback. Think in terms of second-strike only. Surely we've all read enough Cold War thrillers to know the scene where there's a dodgy launch warning, and the men in the silos are on tenterhooks because they've got "use it or lose it" to decide in the next 15 minutes and they don't know if it's a real attack or a flock of birds...

If you're on the moon, you have days to decide. And you don't have to worry about low-bandwidth ELF or shaky teleprinters, you can watch what's happening on the earth below you, and if anyone tries to launch against you then you can see that coming days away too. The moon offers you guaranteed, secure second-strike. And you can't use it for a first-strike either, because your own weapons would take days to get to earth, allowing the Russians to get their retaliation in first.

This was actually the logic behind the Deep Space Force project. (See PROJECT ORION by George Dyson.)

On the other hand, if we're looking for reaction mass for a NERVA, helium compounds (puts on chemistry hat: "did I just say helium compounds? MWAHAHA!") might be useful if they might have a higher boiling point and density than LHe. What we really want is something dense and liquid up to around 300K, that dissociates if you look at it angrily, that carries helium and where all the other ions involved are fast-movers ... something like Helium Fluorohydride, which might theoretically exist and be kinda-sorta short-term stable if anyone was insane enough to synthesize it -- you'd have to play around with ionized helium (meaning: Van der Graaf generators and/or lasers :) and bizarre fluoride groups, so only certified Mad Chemists need apply. Or mad nuclear scientists, because you might be able to get some by bombarding HF with lots of angry alpha particles ...

Or you could just build a magnetic bottle and try to stuff as much He++ into it as the superconducting field will contain ...

The problem with helium-fluorine compounds as propellant mass is that they are likely to disassociate as they pass through the hot reactor core which point you have (for a very short period of time) elemental fluorine at 3000K followed by radioactive Reactorcorium fluoride jetting out the back of your deflagrating launch motor.

I'll conceed to not having considered the Van Allen belts, but I'd suggest that we want to go through then quickly in something light, or in something well-screened, but we don't necessarily have to go that fast if we screen to reduce dosage.

True as far as it goes. If you want to go though the VAB in something made from aluminium foil ;) (see earlier refs to Project Mercury), you need to go fast, but we were also considering alternative technologies such as a "space elevator" where the descending car(s) can be used to supply most (certainly at least 95%) of the Kp that the ascending car(s) need to gain on their way up, so a bit of extra mass just means a need for a stronger cable set.

210, 211
By the time you are the Van Allen Belt(s) altituded, you would be moving faster.
The basic idea was to get up to between 10 and 30km up, above MOST of the atmosphere, without the huge fuel/weight penalty used by a rocket firing vertically from the surface.

Something like this was used in the early 1930's as a method of crossing the ATlantic.
A BIG flying-boat took off, with a smaller one, resting in a cradle on its' back. When the big one got to half-way down its fuel, the little one took off (released its clamp/grips, once the engines were running) and the big one went home. The little one flew on.

If we gonna use excotic fuels why not use liquid sodium (NA) aka liquid metal (need to keep it warm 98 deg. celsius) and mix it with water. That should give us a nice boost as a rocket fuel (or bang). I got the idea after watching illustration of Millenium Falcon. It was using liquid metal that needed to kept at a proper temperature. Do not know about rocket equation though. Good or bad?

Problem about space travel at the moment is lack of energy or control of gravitation. If one or the other is solved, solar system is ours.

In a very far future we could have our planet covered by "beanstalks" and built a sphere around it (planet inside). That way planet is truly terraformed. 25 degrees by day and 18 degrees by night and 12 hour sunshine every part of the globe by day(same lenght of day everywhere). Time zones do stay the same. Sphere is composed of shutters and mirrors. Robots are doing the cleaning and the needed repairs.

I find it difficult to believe that a lunar second-strike missile base is going to be cheaper than a fleet of boomers, though. So it only makes any kind of sense if you assume that the enemy can track every single one of your submarines in real time literally anywhere on Earth.

(And even then, engineering your subs to go to preposterous depths may be cheaper than the lunar concept.)

You hit the nail on the head: "it only makes any kind of sense if you assume the enemy can track ..."

About the only thing boomers emit that they can't silence easily is neutrinos. Luckily for them, neutrino detection is more than a little bit difficult -- and they can go silent if they shut down their reactor and run on batteries. If neutrino detectors ever become militarily useful, we'll just see a new generation of boomers powered by diesel/peroxide and running on much shorter patrols.

Yup. For the exotic-fuels freaks, in the last thread I posted the hypothetical FOOF/HS drive,* with the FOOF synthesis, erm, powered by a NERVA block for extra energy. Ionic fluorine is just such a exciting thing to work with, and the FOOF reaction with sulfide compounds is just so energetic that it looks like an excellent explosive/Orion drive system to me.**

We'll Simply call it Darwin's Putt Putt.

Seriously, though, this is getting depressing. Right now, beanstalks look like better electric generators than transport systems, and the shimmies they'd have to do to stay up would put the best pole-dancers to shame. Are we just going to have to ride rockets up for the foreseeable future? Oh the humanity!

*Not for use on potentially habitable planets.
**or think of a prototype for a disassembler: something that acts as a regenerative catalyst for FOOF production on a surface, plus a supply of the proper ions. Or think of a five-element weapon: F, O, H2SO4, high explosive, catalytic system.

I'd have thought it would be cheaper for the Swiss to tunnel under a hundred miles or so of northern Italy and construct an underwater base in the Med from the underneath than to build a moonbase. Especially if they had to build their own launchers and find somewhere to launch them from :)

Are we just going to have to ride rockets up for the foreseeable future?

It's really not that bad. We still have laser propulsion, maglev catapults, Launch Loops*, ballistic fountains, and whirligig skyhooks** as possible launchers, all of which have the energy supply external to the vehicle, which is what makes them superior to any kind of rocket.

But, yeah, FOOF is so much more exciting! Though as I pointed out upthread, antimatter rockets are even more fun. RELATIVISTIC PIONS!!! ULTRA-HARD GAMMAS!!!

* Did Keith Lofstrom ever trademark the name?
** The ends that dip into the atmosphere don't have to be made of CNT; lower tensile strength sections at the tips should work so they could be immune to the air friction.

You know, I've been toying with the idea of using the Feynman diagram for a electron/positron collision as the blueprint for a time machine. Simply turn your machine into an antimatter mirror image, and it will go back in time. All you have to do is instantaneously shove it into its own pocket universe for the trip backward, to keep it from interacting with matter...

The amusing part of this is what the time machine's trip looks like in the universe's view: When it starts in the future, the ship disappears in a e=2mc^2 burst of gamma rays. In the past, the ship and its anti-copy spontaneously appear as the pocket universe merges with the main universe.

Where would you launch such a time machine? Back side of the Moon! And just think: if you could capture some percentage of the energy from each time machine launch, you could beam the power to the Earth and supply most of civilization's power needs. There's a good use for the Moon. All we have to do is invent that time machine and pocket universe technology.

Actually, that's such a good idea, I'm going to see what I can do with it.

Superconducting QUantum Interference Devices or SQUIDs, detect very very small changes in electric and magnetic fields. You might find such devices at the bottom of the ocean (shhh!) on something called SOSUS which does not exist or even in free-standing sea-bottom monitoring stations powered by radiothermal isotope generators which also do not exist (shhh!) which can be deployed and serviced by US ROV-equipped SSGN intelligence-gathering and special ops submarines (which do exist). But shhh! anyway.

For more easily handleable NERVA reaction mass, you could point to lithium hydride. The lithium is pretty much dead weight as reaction mass, giving you a fuel that's 7/8ths pointless, but hey, at least it's solid at room temps. The exhaust is a comparatively safe gaseous monatomic lithium and hydrogen mix, which might well combust back to a nice safe solid again. If you're lucky.

There's a similarity here to the 'million dollar NASA space pen/Soviets used a pencil' myth. The Soviets ran their NTRs off ammonia. It's usefully storable as a liquid, the exhaust is not fantastically poisonous (just radioactive), and only 14/17ths dead weight.

Obviously, helium fluorohydride gets my vote, both for the lulz and because I'm in a different hemisphere to most launch sites.

I've mentioned this before.
I don't think it violates conservation-of-momentum, because its' mode of operation can be thought of as more like an QM hydraulic jack.
However, it is obvious that there are serious practical engineering problems in getting such a device to work effectively, even assuming that Shawyer is correct, as I am for the purposes of this argument, at least.
Those problems are:
The resonance chamber must be rigid, really rigid.
Said resonance chamber will work much better if it is superconducting - copper really is inferior.
So we have to have a rigid, superconducting (do-able at liquid-Nitrogen temperatures?) resonance chamber, mounted in a moving vehicle.

#216 - If you're unfamiliar with the flying boat referenced, run a web search or look on Wikipedia for "Mercury - Mayo composite". The main use of the machine(s) was a mail service, rather than passengers or air freight though.

Also, there's a whole bunch of us singing off the same sheets regarding the use of aircraft as lifters to get to maybe 50km altitude, and some form of "conventional rocket" or lifting body to get from there to stable low Earth orbits.

The reference to pace for getting through the VAB I think was more sort of "why you can't use a beanstalk to geosynchronous even if you can buld one" than anything else I think. Hence my comments about being able to shield beanstalk cars without incurring the sort of reaction mass multiplier penalties a rocketry solution has to avoid.

You know, I've been toying with the idea of using the Feynman diagram for a electron/positron collision as the blueprint for a time machine.

Here's a totally legal one, on a par with Boltzmann Brains. There is a nonzero probability that a copy of you will coalesce out the vacuum with this important difference: it is a copy of you from 10 years into the future. There's nothing in the rules that says this is impossible. Quizzing the copy reveals that, yes, they have the exact details down; if they so-and-so won the World Cup in 2011-2015, that's who won. Ditto for stock market tips. There's a slight flaw here that I can't quite put my finger on . . .

It is to break the exponent in the rocket equation into smaller chunks. If an 18 km/sec trip could be broken into smaller hops of say, 4 to 5 km/sec per leg, the trip can be accomplished with smaller, simpler, reusable vehicles.

Yes. Good call. I should have been more explicit and mentioned that in the Asimov story, multiple stages were indeed used; in fact, the story starts off with our intrepid space rats prowling the ether and on the lookout for discarded stages to scavenge. All of which is to say - and this should be obvious - that bleeding-edge state-of-the-art engineering which wrings 10 km-sec out of a single stage is going to cost more to design, build, and maintain than a machine which has two stages, each of which has 5 km-sec of reserve. As you point out.

Well, the slight flaw is that you can't exactly quiz that self. But I assume that what you really wanted to do was to arrange for your consciousness vector to jump into a BB (actually, you gave the thing a full body to go along with the brain, which makes it a BB&B, I guess) with that knowledge, have time enough to process that, and then have it jump back into the 'real' you slightly before the BB&B dies in freezing agony.

But if you can manage that trick, you can probably also control where your consciousness vector goes between quantum-generated multiple worlds, so you can probably get richer quicker just by finding a high-odds wager that's sensitive to quantum-level events and making sure you only go to the branches that lead to your winning.

Well, the slight flaw is that you can't exactly quiz that self. But I assume that what you really wanted to do was to arrange for your consciousness vector to jump into a BB (actually, you gave the thing a full body to go along with the brain, which makes it a BB&B, I guess) with that knowledge, have time enough to process that, and then have it jump back into the 'real' you slightly before the BB&B dies in freezing agony.

I don't see why you can't ask the copy questions about the "future". What's your reasoning here?

The copy isn't here; it's several quintillion( Note: this is a vast underestimate.) years in the future and at a location an arbitrarily number of maximal normal-universe widths distant from here. And in fact the things probably don't last long enough to form complex thoughts like the answer to your question before at least noticing that they're dying in freezing vacuum agony, so we're actually talking about a sequence of BB's, each one of which is equally distant from one another in space and time. So the only way to get any information out of them is to become (or, as in the main BB argument, to always have been) a consciousness state characterized by a set of brain 'software' that need not be running on a single physical brain in real time but can be emulated by the pre-death states of a particular sequence of the BBs (and is, going back to the normal BB argument, by the principle of mediocrity, far more likely to be doing just that.)

My father used to say: "If I had ham, I could have ham and eggs. If I had eggs."

Well, if I had commercially viable He3 fusion reactors, I could have cheap electrical power and a profitable Moon Base. If I had a profitable Moon Base.

Except that, chicken-and-egg problem swept under the rug, commercial fusion probably will be here eventually (not date predicted, on the record). And a Moon Base is also inevitable, albeit Mandarin or Hindi might the be dominant language.

The detailed NASA-funded and independent R&D-budgeted studies that I did at Rockwell International with a Mining Chemistry genius, and the former facility head of the world's northernmost mine, convinced me that the Lunar He3 scenario is on the edge of plausible.

The He3 is very shallowly embedded in regolith from the unobstructed solar wind. Microwave heating to a few hundred degrees of the upper centimeter drives off far more than half, easily captured.

One Shuttle Payload bay full of He3, if we had had and eggs and a commercial fusion reactor of the right kind, would fuel the world for years. Not that space shuttles will land on lunar runways (as one dead-serious and sickly ignorant presentation at a Space Industry conference showed. Hello, wings and no air means no lift. No, the He3 can be slung from the surface into lunar orbit by any number of cheap automated means, or even, with more finesse, to earth orbit for harvesting.

Edward D. McCullough is a retired principal scientist at The Boeing Company. He received his professional training in nuclear engineering through the U.S. Navy, and Bettis and Knowles Atomic Power Laboratories (gaining his Certification for Nuclear Engineering at Pearl Harbor Naval Shipyard in 1975).

Mr. McCullough focused on concept development, experimental chemistry, and advanced technology at Rockwell Space Systems Advanced Engineering and at the Boeing divisions of Phantom Works and Integrated Defense Systems. He has researched innovative methods to reduce the development time of technologies and systems from 10 to 20 years down to 5 years. He has experienced successes in the area of chemistry and chemical engineering for extraterrestrial processing and photonics for vehicle management systems, and integrated vehicle health management and communications. He has led efforts for biologically inspired multi parallax geometric situational awareness for advanced autonomous mobility and space manufacturing.

Mr. McCullough has developed several patents, including patents for an angular sensing system; a method for enhancing digestion reaction rates of chemical systems; and a system for mechanically stabilizing a bed of particulate media.

Mr. McCullough is Chair Emeritus of the AIAA Space Colonization Technical Committee, a member of the Board of Trustees for the University Space Research Association, a member of the Science Council for Research Institute for Advanced Computer Science, and a charter member of the AIAA Space Exploration Program Committee. Mr. McCullough previously served on the NRC Committee to Review NASAÃ¢â‚¬â„¢s Exploration Technology Development Programs, and the Planning Committee for the Workshop on Research Enabled by the Lunar Environment.

Really. Ask him. And let us know if that sheds light on the fusion-powered ham and eggs in some future electric frying pan.

The copy isn't here; it's several quintillion( Note: this is a vast underestimate.) years in the future and at a location an arbitrarily number of maximal normal-universe widths distant from here.

I must be misunderstanding something here; I'm saying that there is a nonzero probability your ten-years-advanced copy will condense out of the vacuum sometime in, oh, the next couple of days. This doesn't really have that much to do with Bolztmann Brains and I probably shouldn't have mentioned them.

Oh. Well, then you're down to the stumbling point of making something with a probability so small that highly advanced math training is required to remotely comprehend the number that is 1 divided by that probability happen reliably. Which I guess you could still manage with the 'propel your consciousness vector on a directed path through the multiverse created by quantum-indeterminate events' method...

Minor point @ 240
Jonathon vos Post ....
" ...albeit Mandarin or Hindi might the be dominant language."
Erm, slight problem(s)...
Mandarin is ONE dialect of Chinese - one WRITTEN language, several spoken ones, based on cuneiform, and still not as flexible as an alpahbetic script.
"Hindi" - uh?
India (and even Pakistan) have many languages, all competeing. Result that the language of the governing, professional and middle classes, and that in which ALL technical business is done is ENGLISH.
I'm assuming, especially from yuour posts, that you are American, and therefore ignorant of anything at all outside the USA, which seems to be the normal state of affairs in even educated US citizens.

Oh course, there's a non-zero, and higher, chance that what condenses out is something that appears to be your ten-years-advanced copy, but isn't. Quite. And which saw England win in 2014. Or France. Or Germany. Or Italy. Or ...

Just in case anyone is still interested in highly corrosive, hot and radioactive conceptual propulsion ... How about the Cavity Reactor Critical Experiment ...

CRCE

Located at TAN, CRCE was an outgrowth of a program begun by NASA in the 1960s to investigate the propulsion of space rockets by nuclear power, offering the possibility of much greater thrust per pound of propellant than chemical rockets. The concept for the cavity reactor core was that the uranium would be in a vapor, or gaseous, state. Hydrogen propellant flowing around it would theoretically attain much higher temperatures—up to 10,000° F—than in conventional solid core rockets. The experiments at TAN used simulated
hydrogen propellant and produced data on the reactor physics feasibility of a gaseous core being able to go critical.

The core was uranium hexafluoride (UF6); the experiments were all done at the relatively low temperature
of about 200° F. In the proposed ultimate application, the ball of uranium gas would be held in place
by the hydrogen flowing around it, something like a ping-pong ball suspended in a stream of air. Uranium
core temperatures as high as 100,000° F were considered possible.

Temperatures are about 16 times higher and molecular weight 9 times lower than in ordinary LH/LOX engines. Those have an exhaust velocity of about 4000m/s - the CRC would have 5 times that 20.000m/s. Easily enough for SSTO and probably SSTM (single stage to mars) for that matter. *IF* you manage to get decent some decent thrust.

Unfortunately a mere 100,000° F are not enough to dissociate molecular hydrogen. Doubling the temperature would do that and uncharacteristically also double the exhaust velocity. Welcome to ion-engine territory.

Yes, if you're being polite to the Chinese (always a good idea), Mandarin is a dialect, not a language.

As one linguist noted, languages are dialects with guns.

Since the Chinese have lots of guns, it is their right and privilege to insist that all the various Chinese dialects are dialects, not separate languages, even though these dialects have less in common with each other than, say, English and German.

Yes, if you're being polite to the Chinese (always a good idea), Mandarin is a dialect, not a language.

As one linguist noted, languages are dialects with guns.

Since the Chinese have lots of guns, it is their right and privilege to insist that all the various Chinese dialects are dialects, not separate languages, even though these dialects have less in common with each other than, say, English and German.

I'm still getting my head around how you balance a vortex of really heavy gas stably in the middle of a fast stream of light gas. Without elementals or Maxwell's Demon getting involved. That hot uranium hexafluoride must have a glacial coefficient of diffusion.

So you have demonstrated by most cromulent logic that Greg Tingey is, in fact, an American. What a turn up for the books. He'll have to be deported, of course.

The question the OP should have asked is: Why is it cheaper to use clones to mine HE3? Particularly since human cloning is a generation away and fully replicating the personality/knowledge of a specific human is at least one, maybe two generations beyond that.

Logistic growth is one possibility. Another is oscillation below the limits. Which is more likely? Consider that our economics is entirely dependent upon growth, and no one has invented an economics that works in the flat part of the logistic curve. Such an economics is possible, but I doubt people would like it. I think oscillation (i.e. collapse and regrowth) is more likely. I find it strange that almost no economists are working on non-growth economics. Herman Daly has written books describing the problem, but as far as I know he has never presented a solution.

Alex Tolley, reducing insolation only works up to the point of 100% blockage, which is what you would have to do if you were generating 120,000 TW on Earth from fusion or whatever. To generate more than 120,000 TW you need to find a way to make the Earth a more efficient radiator. You could reduce greenhouse gases below 280 ppm, but plants would suffer (perhaps they are already indoors, because the sky is black because of the 100% blockage of sunlight, and so CO2 can be provided indoors only). You are talking about a pretty radically altered planet in any case to go anywhere near 120,000 TW of fusion. Of course, to go from 18 TW to 120,000 TW takes only 298 years of 3%/year growth. On the scale of history (about 10,000 years old), that's rather soon.

The Moon should be a destination for research and exploration. But it remains that once humans leave a gravity well there is little reason to go back down one.

After reading through the comments here, it strikes me that any (economy) in space, as in mining, may hold little value to earth bound economics. But I would wager my left foot that it would be of huge value to a space based economy.

Once we have build our first habitable space arcology, the idea that earth should supply all the raw materials is pointless. Asteroids and other low gravity sources of raw materials make far more sense.

Its not the raw materials that a space economy would trade with earth. Its the advanced technology that can only be created in zero gravity that will be the commodity. Earths commodity in this economy if far more likely to be biological. (biodiversity)

While I agree that He 3 is not the magic pixie dust, it is for entirely different reasons that show Charlie hasn't got a cluebat about the current state of fusion research.
Firstly, ITER is a waste of time and money. Dr. Bussard, for instance, said before his death that it will never achieve net power, but will produce some great science. Conversely, Bussard's own project, Polywell inertial confinement, has achieved subnet fusion of D-D and is researching proton-Boron11 fusion and its potential for net power production. Proton-Boron11 fusion, like He3 fusion, is aneutronic, but has a lower coulomb pressure so it is easier to achieve, and the two fuels, being oppositely charged, are going to be easier to ram together. Word on his heir's completion of the WB-8 stage of the project, funded by the US Navy, will be forthcoming this winter.
Now, using protons and boron 11 for fuel, both are cheap, relatively plentiful, so with these fuels there is no reason to crank up the He3 mines on the moon.
Now that that is said, the real economic reason to develop in space is martian steel. You may recall all the little blue spherules that the mars rovers found on the surface everywhere. These are hematite nodules of high purity. This establishes the economic rationale for settling Mars: to collect hematite, refine it into martian steel, to be delivered to Phobos, L1 or LEO at a price less than 10% of the cost of launching it from Earth surface, while still charging 100 times more than current retail value on Earth.

No, but they suffer from two problems: (a) the unobtanium requirement (and other trifling engineering obstacles like, er, how to power a climber thousands of kilometres overhead economically and efficiently enough to make GTO in something less than months; how to survive transiting the Van Allen belts slowly: how to deal with rogue satellites and other debris: and so on) and (b) the fact that almost all the launcher development money is currently going into approaches that are known to work, i.e. disintegrating totem poles.

Robert L. Forward came up with an interesting proposal to reduce the intensity of the Van Allen belts using charged, orbiting tethers and is the kind of useful space infrastructure that we should be building before we talk about going back to the Moon or to Mars or wherever.

It's a real pity that the Bush regime wasn't convinced that the 9/11 terrorists came from the Moon. If they had been the US probably would have launched a massive space program to invade the moon and make it safe for freedom lest the terrorists win. Sure, this would have been completely insane, but no more so than invading Iraq with the goal of turning into a functioning democracy or the latest project of the neocons, bombing Iran to put a stop to their nuclear program and institute regime change. Plus it would have been a lot cooler.

I was working as a student programmer at the US Department of Energy's Argonne Labs around '76. At the time, all the nuclear engineers were pretty confident that reliable and commercializable fusion power was only 20 or 30 years away.

It's now 34 years later. We still haven't managed a single net-energy-positive fusion reaction in the lab AFAIK. But commercial fusion power is still only 30 years away!

Yeah, but how hard have we tried? Energy research budgets have been static or decreasing since the 1970s. If we want fusion, or solar or anything we're going to have to spend a lot of money for a long time to get it. Say 20 billion a year for 30 years or so and not the paltry dribs and drabs that we've been spending since the 50s. Sure, 600 billion dollars is a lot of money, on the other hand the US has pissed away that much in Operation Enduring Middle Eastern Clusterfuck over the last decade and doesn't have anything to show for it except dead and crippled soldiers and increased instability and chaos in the region.

While I agree that He 3 is not the magic pixie dust, it is for entirely different reasons that show Charlie hasn't got a cluebat about the current state of fusion research.
Firstly, ITER is a waste of time and money. Dr. Bussard, for instance, said before his death that it will never achieve net power, but will produce some great science.

I'd fund it for that reason alone. But hey, I'm crazy that way.

Conversely, Bussard's own project, Polywell inertial confinement, has achieved subnet fusion of D-D and is researching proton-Boron11 fusion and its potential for net power production. Proton-Boron11 fusion, like He3 fusion, is aneutronic, but has a lower coulomb pressure so it is easier to achieve, and the two fuels, being oppositely charged, are going to be easier to ram together. Word on his heir's completion of the WB-8 stage of the project, funded by the US Navy, will be forthcoming this winter.

Except for the fact that there are physicists who claim that the fusor won't be able to produce net energy because of excessive Bremsstrahlung losses. From the Wikipedia article on fusors.

One oft-presented concern is Bremsstrahlung (German for "braking radiation"). In Fundamental limitations on plasma fusion systems not in thermodynamic equilibrium, Todd Rider shows that a quasineutral isotropic plasma will lose energy due to Bremsstrahlung at a rate prohibitive for any fuel other than D-T (or possibly D-D or D-He3). This paper is not applicable to IEC fusion, as a quasineutral plasma cannot be contained by an electric field, which is a fundamental part of IEC fusion. However, in a further paper, "A general critique of inertial-electrostatic confinement fusion systems", Rider addresses the common IEC devices directly, including the fusor. In the case of the fusor the electrons are generally separated from the mass of the fuel isolated near the electrodes, which limits the loss rate. However, Rider demonstrates that practical fusors operate in a range of modes that either lead to significant electron mixing and losses, or alternately lower power densities. This appears to be a sort of catch-22 that limits the output of any fusor-like system.

We probably won't know until we build a few and test them out, which would be a worthwhile thing to do solely from a basic science standpoint.

Now, using protons and boron 11 for fuel, both are cheap, relatively plentiful, so with these fuels there is no reason to crank up the He3 mines on the moon.
Now that that is said, the real economic reason to develop in space is martian steel. You may recall all the little blue spherules that the mars rovers found on the surface everywhere. These are hematite nodules of high purity. This establishes the economic rationale for settling Mars: to collect hematite, refine it into martian steel, to be delivered to Phobos, L1 or LEO at a price less than 10% of the cost of launching it from Earth surface, while still charging 100 times more than current retail value on Earth.

OK, let's assume that Todd Rider is wrong about the Bremsstrahlung losses in a fusor such as the Polywell and that Proton Boron 11 fusion is possible, and I have to say that I'd love for this to be true, and that energy costs plummet. Given this scenario what is easier: A) traveling to Mars to mine Martian hematite nodes by flinging them out of the Martian gravity well, across a few million miles of space and then decelerating them and dropping them into Earth's gravity well or B) mining minerals on earth by by heating low grade ores that are commercially unviable with current technology to a plasma, dumping them into a huge mass spectrograph and then collecting the output, which could even be refined by isotope at the other end. Bear in mind that we already know how to do this, in fact the United States did this almost 70 years ago to separate U-235 from U-238 for the Manhattan project. It was difficult and incredibly expensive, but it did work and we know a lot more about how to do this than we do about how to travel to Mars, mine hematite, fling it out of the Martian gravity well, etc, etc, etc.

Consider that our economics is entirely dependent upon growth, and no one has invented an economics that works in the flat part of the logistic curve. Such an economics is possible, but I doubt people would like it.

Actually, the flat part of the curve was the norm for many thousands of years. Feudalism is one such example of an economic setup that was essentially zero sum. The scary part is, I'm not entirely certain that zero-sum economics doesn't force some sort of Feudalism or its equivalent on the masses. The guys at the top didn't get there by being generous, fair, or engaging in meritorious conduct for the most part. And while they may not mind (much) people rising in the ranks to join them, they will definitely fight tooth and claw to keep what is "theirs".

Ahem: Feudalism was not an economic system -- it was a political/military solution to managing a society with limited resources in a state of what we, today, would call constant warfare.

Various economic systems emerged in feudal and post-feudal societies, including subsystems like the huge church holdings in England (ever wonder what Henry VIII got from compulsorily nationalizing the monasteries, besides a quickie divorce?), or the guild systems, and so on.

But feudalism itself was about a hierarchical system of obligations and service that was there to hold together a state where the smallest functional unit was a small village of peasants supporting a knight and his charger and men-at-arms -- the equivalent of an APC or light tank, plus CO and squad of troops, in modern terms. Go back to the 11th century, when this form emerged in England, and you'll note that the British isles still had several warring kingdoms and had been under repeated invasion/colonial attack by vikings a century earlier. Feudalism was a bottom-up solution to militarizing a society to survive in the face of permanent warfare; it only began to break down when protracted outbreaks of peacetime allowed the high-end nobles and the mercantile classes to begin to focus on wealth collection/creation. (In Tokugawa-era Japan as much as in feudal England ...)

You're of course correct, but as I was typing it suddenly occurred to me that I didn't really know the name of economic system typically associated with Feudalism even if I could describe it in a paragraph or three. So I just went sloppy and added "some sort" and "or it's equivalent". The one thing I would add to your "hierarchical system of obligations and service" was that it was also, above all, hereditary. Them that had were disinclined to share with them that didn't, as doing so would only make them comparatively worse off. One of the hazards of being the eldest son, iirc.

In any event, I suspect something very much like a de facto Feudalism would be the dominant social structure in an era of essentially zero economic growth.

#265.2 - If you didn't actually know this (and I'm sure Charlie does), about 10 years prior to the Dissolution of the Monasteries, the RC Church in England (distinct from the CofE which didn't exist, and considers holdings in a specific geographic area only) was "richer than the King".

Thats a point about something like feudalism in a zero growth economy, because we can already see what happens in situations where steps are not taken to readjust the playingfield. I.e. the rich get richer and the poor generally stay poor. The market isn't free, and all that.

(Nb I am not an economist, merely know more history of economics than gordon brown and his speechwriters)

It's not even just a question of the pathetic budgets made available for fusion research (although since the total amount the world is planning to spend on that over the next decade or so is less than the UK's share of spending on the Eurofighter debacle...). There's a general lack of political interest in progress, too; JET had provided all the information necessary to start construction of ITER by about twenty years ago, but then there was a lot of arguing about who was paying for which bits, and what country would be privileged to provide the site, and... construction sort of just about got started in 2008.

Fusion might well have been 30 years of hard work away in the 1970s; I'd say that the last 25 years worth of heavily politicised mucking about probably count as maybe five years worth of hard work.

Actually, medieval economics is fascinating, because the word you're looking for is "sustainable," not "zero growth." When everything that matters has to be made locally, you get a very different economy than when you're getting stuff from everywhere and fretting about the freight bill.

The Middle Ages was a time when, for example, glass-making factories in the UK had to own their own woodlands, where they sustainably harvested the wood for the charcoal to feed their furnaces. Without those trees, no glass. This all broke down when colonialism got people thinking that they could get the wood from the colonies for cheaper.

The neat thing about medieval economics were the complex social and economic relationships that let people live on a limited resource base. Many of the old records of how they did it still exist, but except for antiquarians and ecological historians, they aren't read much. Oliver Rackham's books are a good place to start, if you're interested in this.

The key thing in a sustainable society is that there are limits on wealth and poverty. Most people get by, that's true. However, the rich couldn't afford to take too much from the poor, because if the people had nothing left to lose, the rich had everything to lose and not enough ways to defend themselves.

As it happens I know a wee bit about the medieval period (I've managed to replicate part of the bronze casting technology of the time) but havn't read so much about the economics, so I'll have to look up Oliver RAkham. The interesting thing as well though is that although they recycled a lot of metal (hence the lack of nice finds to tell us what they made out of what) it wasn't exactly sustainable there either. If you're thinking long term, ie thousands of years, we'll have real trouble being sustainable.

The rich couldn't afford to take too much from the poor? Sort of, in that some of the plundering was balanced by charitable giving and alms and suchlike, and the destruction of the monasteries took away a large safety net; but I would like to see some comparisons between the income disparities of that era and now. But as you are no doubt aware, there were a variety of social and phschological methods of keeping people in place, ie the notion of the chain of being, of the need for order and kings and nobles, all of which helped maintain an inequable balance. Hmm, now where have I heard the idea that the rich deserve their riches due to work and therefore by extension their innate higher quality?

It does depend on how you run the numbers, Guthrie. I mean, lets assume the average peasant lived on the modern equivalent of $1-2 dollars per day.

How much was the pope worth, on the assumption that he owned all of the Roman Catholic Church? The European population was in the millions, so perhaps the Roman Catholic Church was a billionaire.

Is that equivalent, to, say, the trillions of dollars ($5,000,000,000,000) that someone owes somebody on the latest housing debacle? There's that much money floating around in the US right now, and in China.

Part of this is that there are a lot more people, and part of it is that people are monetizing things like risk forecasts, so money is becoming less and less real. Remember that usury was illegal in Medieval times (which might have been a good thing, considering how bad we are at risk forecasting).

Part of the problem with "non-zero" economics is that often, the system is non-zero because the resources are extracted from some other place (e.g. a colony or undercompensated poor country), or someone else's involuntary labor (I'm thinking of slave economies here, but the factories in various countries are little better). The >0 result we experience is because someone else is <0.

One of the interesting things is that progress is a bad thing for hundreds of years. By a lot of measures, the average person in England was worse off in 1800 than in 1550, particularly if they lived in an urban or industrial area. Eventually, you get a pay off, but it's not a happy road. (For example, think about the fact that almost everything that actually works in modern medicine is only around 150 years old at most.)

As for sustainability, the cities of northern Europe were already dependent on foreign grain in the High Middle Ages. (French grain for the French and those who were willing to be vulnerable to French pressure; Polish for England and others. Well, I guess, French grain and treasure for the English when things were going well in the Hundred Years War.) Whether an even less urbanized England could have supported itself probably depends on how bad climate variations got.

In the specific case of theindustrial evolution and the destruction of previous ways of life by the introduction of more efficient production methods and loss of commons and suchlike, I am amenable to the idea that progress isn't always good.
There was however a lot of progress made during the medieval period, of which I can't think of anything as bad as the previous example. The introduction of better ploughs, more horses, wind and water mills, the latter being used for fulling cloth and hammering metal, not to forget improvements in pyrotechnology, glass making, chimneys, paper, reading, writing, mining etc etc. But since the changes were a bit slower they could be accomodated moreeasily within existing structures, although there was plenty of political and religious upheaval during the period.

I don't disagree. There's a lot to be said for a mold-board plow, for instance. Or clean water.

But there's also something to be said for sustainability.

One of many examples: Right now, something like 30% of our species is dependent on nitrogen fixed into fertilizer using energy from fossil fuels. Originally, the Bessemer process was designed to save humanity from a predicted era of famine, because back around 1900, all of the known sources of mineral nitrogen were quickly being tapped out. Now, we have many, many more people than we did in 1900, famine is still on the horizon, and thanks to that wonderful Bessemer process, we can afford cheap guns and high explosives in enormous quantities, something that made both World Wars possible and made the AK-47 a more potent weapon (collectively) than the atomic bombs we used on Japan.

Progress? I probably wouldn't be alive if it weren't for those fertilizers, but at the same time, that form of nitrogen fixation isn't sustainable, and when it crashes, the resulting famine will be enormous, dwarfing the problem it was originally intended to solve. And war will change radically too, as bullets and explosives become expensive again.

Important point: He-3 mostly aneutronic reactions are only useful if you need your power plant core structure to not get irradiated. They avoid disposing of a few tons of radioactive metal at the end of plant useful life.

This is not fissile waste. It's transmuted iron (and carbon and stuff). Burying it for a thousand years is more than enough time for it to cool down.

D-D and D-T reactions are far more economical on multiple fronts. For one, the fusion reactor runs a lot, lot cooler on D-T or D-D than on He-3, so the energy output per unit magnet is far higher.